-enforcement  agencies to co-operate as never before;  even  rogue states
which had promoted  political terrorism were unable to tolerate  this random
and wholly unpredictable variety.
     The chemical and biological  agents used in these attacks -- as well as
in earlier forms of warfare --  joined the deadly collection in Pico.  Their
antidotes, when they existed, were  also stored with them. It was hoped that
none  of this material would ever concern humanity again -- but it was still
available, under heavy guard, if it was needed in some desperate emergency.
     The  third category  of items stored in the Pico  vault,  although they
could  be  classified as  plagues, had never  killed  or  injured  anyone --
directly. They had  not even existed  before the late twentieth century, but
in  a few decades they  had done  billions of dollars' worth of damage,  and
often wrecked lives as effectively  as any  bodily illness could  have done.
They were the diseases which attacked  Mankind's newest  and  most versatile
servant, the computer.
     Taking  names  from  the  medical  dictionaries  --   viruses,  prions,
tapeworms -- they were  programs that often mimicked, with uncanny accuracy,
the behaviour of their organic relatives. Some  were harmless -- little more
than playful jokes,  contrived  to surprise or amuse  Computer  operators by
unexpected messages and images  on  their visual displays.  Others were  far
more malicious -- deliberately designed agents of catastrophe.
     In most  cases their purpose  was  entirely mercenary;  they  were  the
weapons  that  sophisticated  criminals  used  to  blackmail the  banks  and
commercial  organizations  that now  depended  utterly  upon  the  efficient
operation of  their computer systems. On being warned that their data  banks
would  be erased automatically at a certain time,  unless they transferred a
few megadollars to some anonymous offshore number, most victims  decided not
to  risk  possibly irreparable disaster. They paid  up  quietly, often -- to
avoid public or even private embarrassment -- without notifying the police.
     This  understandable desire  for privacy made it easy  for  the network
highwaymen to conduct their electronic  holdups: even when they were caught,
they were treated gently by legal systems which did  not know how to  handle
such  novel crimes -- and, after all, they had  not really hurt anyone,  had
they? Indeed, after  they had served  their  brief sentences,  many  of  the
perpetrators were quietly hired by their  victims, on the old principle that
poachers make the best game-keepers.
     These computer criminals were driven purely by greed, and certainly did
not wish to destroy the organizations they preyed upon: no sensible parasite
kills its host. But  there were other, and  much  more dangerous, enemies of
society at work...
     Usually,  they  were  maladjusted individuals  -- typically  adolescent
males -- working entirely  alone, and of course in  complete  secrecy. Their
aim  was to create programs  which would  simply create havoc and confusion,
when they had been spread over  the planet by the world-wide cable and radio
networks, or on physical  carriers such as diskettes and  CD ROMS. Then they
would enjoy the resulting chaos, basking in the sense of power it gave their
pitiful psyches.
     Sometimes, these perverted  geniuses  were  discovered and  adopted  by
national intelligence agencies for their own  secretive purposes -- usually,
to  break into the data banks of their rivals. This was  a  fairly  harmless
line of employment, as the  organizations concerned did at least  have  some
sense of civic responsibility.
     Not  so the apocalyptic sects, who were delighted to discover this  new
armoury, holding weapons far  more effective, and more  easily disseminated,
than  gas or germs. And much  more difficult to counter, since they could be
broadcast instantaneously to millions of offices and homes.
     The collapse of  the New York-Havana  Bank in  2005,  the  launching of
Indian nuclear  missiles in 2007  (luckily with their warheads unactivated),
the shutdown of Pan-European Air Traffic Control  in 2008, the  paralysis of
the  North American  telephone  network in that same year -- all  these were
cult-inspired  rehearsals   for  Doomsday.  Thanks  to  brilliant  feats  of
counterintelligence  by  normally uncooperative, and  even warring, national
agencies, this menace was slowly brought under control.
     At  least,  so it was generally  believed:  there had  been  no serious
attacks at the very foundations of society for several hundred years. One of
the chief weapons of victory had been the Braincap -- though there were some
who believed that this achievement had been bought at too great a cost.
     Though arguments over the freedom  of  the Individual versus the duties
of the State were old when Plato and Aristotle attempted to codify them, and
would  probably continue until the end of  time,  some  consensus  had  been
reached in the Third Millennium. It was  generally agreed that Communism was
the most perfect form of government;  unfortunately it had been demonstrated
--  at the cost of some  hundreds  of millions of  lives -- that it was only
applicable  to  social  insects,  Robots Class II,  and  similar  restricted
categories.  For   imperfect  human   beings,  the  least-worst  answer  was
Demosocracy,  frequently  defined as  'individual  greed,  moderated  by  an
efficient but not too zealous government'.
     Soon after the Braincap came into  general use, some highly intelligent
--  and  maximally  zealous  --  bureaucrats realized that  it had  a unique
potential  as  an early-warning system.  During the setting-up process, when
the new  wearer  was being mentally  'calibrated' it was possible to  detect
many forms  of  psychosis before  they  had a  chance of becoming dangerous.
Often  this suggested  the best  therapy, but when no cure appeared possible
the  subject  could  be  electronically tagged  --  or,  in  extreme  cases,
segregated  from society. Of course, this mental monitoring could  test only
those  who  were fitted with  a  Braincap  -- but by  the end of  the  Third
Millennium this was as essential for everyday life as the personal telephone
had  been  at its  beginning. In fact,  anyone  who  did not  join  the vast
majority was automatically suspect, and checked as a potential deviant.
     Needless to say, when 'mind-probing', as its critics called it, started
coming  into  general use,  there  were cries  of outrage from  civil-rights
organizations;  one  of  their  most  effective  slogans  was  'Braincap  or
Braincop?' Slowly -- even reluctantly -- it  was accepted that  this form of
monitoring was a necessary precaution against far worse evils; and it was no
coincidence  that with the general improvement  in mental  health, religious
fanaticism also started its rapid decline-
     When the long-drawn-out war against the  cybernet criminals  ended, the
victors found themselves owning an embarrassing collection of spoils, all of
them utterly incomprehensible to any past conqueror. There were, of  course,
hundreds  of  computer viruses, most of them very  difficult to  detect  and
kill. And there were some entities -- for want of a better name -- that were
much  more  terrifying. They were  brilliantly  invented  diseases for which
there was no cure -- in some cases not even the possibility of a cure
     Many  of them had  been linked to great mathematicians  who would  have
been  horrified  by this corruption of  their discoveries. As it  is a human
characteristic to  belittle a  real danger by  giving it an absurd name, the
designations were often facetious:  the Godel Gremlin, the  Mandelbrot Maze,
the Combinatorial  Catastrophe, the Transfinite Trap,  the Conway Conundrum,
the Turing  Torpedo,  the  Lorentz Labyrinth,  the Boolean Bomb, the Shannon
Snare, the Cantor Cataclysm...
     If  any  generalization was  possible,  all these  mathematical horrors
operated on the same principle. They did not depend for  their effectiveness
on  anything as  naÎve  as  memory-erasure  or  code  corruption  -- on  the
contrary. Their approach was more subtle; they persuaded  their host machine
to initiate  a program  which  could not be completed  before the end of the
universe, or  which --  the Mandelbrot  Maze  was the  deadliest  example --
involved a literally infinite series of steps.
     A  trivial  example  would  be  the calculation  of  Pi,  or any  other
irrational number. However,  even  the  most  stupid electro-optic  computer
would not fall into such a  simple trap:  the day had long since passed when
mechanical  morons would wear out their  gears, grinding them to  powder  as
they tried to divide by zero...
     The  challenge  to  the demon programmers was to convince their targets
that the task set them had a definite conclusion that  could be reached in a
finite  time.  In the battle of wits between man (seldom woman, despite such
role-models  as Lady Ada Lovelace, Admiral Grace Hopper and Dr Susan Calvin)
and machine, the machine almost invariably lost.
     It would have been possible --  though in some cases difficult and even
risky -- to  destroy the captured  obscenities by ERASE/OVERWRITE  commands,
but they represented an enormous  investment  in time and  ingenuity  which,
however misguided, seemed a pity to waste. And, more important, perhaps they
should be kept  for study, in some secure  location, as  a safeguard against
the time when some evil genius might reinvent and deploy them.
     The solution was obvious. The  digital demons  should  be  sealed  with
their chemical and biological counterparts,  it  was hoped  for ever, in the
Pico Vault.

     37 Operation Damocles

     Poole  never had  much  contact with the team  who assembled the weapon
everyone hoped would never have to be used. The operation --  ominously, but
aptly, named Damocles --  was so highly specialized that he could contribute
nothing directly,  and he saw enough  of the task force to realize that some
of them might almost belong to an alien species. Indeed, one  key member was
apparently in a lunatic asylum -- Poole had been surprised to find that such
places  still existed -- and Chairperson Oconnor sometimes suggested that at
least two others should join him.
     'Have you  ever  heard of  the Enigma  Project?' she remarked to Poole,
after a  particularly  frustrating session.  When he  shook  his  head,  she
continued: 'I'm surprised -- it was only a few decades before you were born:
I  came across it while when  I was researching material for Damocles.  Very
similar  problem -- in one of your wars, a group of brilliant mathematicians
was  gathered  together,  in  great  secrecy,  to  break  an  enemy  code...
incidentally, they built  one of the very first real computers, to make  the
job possible.'
     'And there's  a lovely story -- I hope it's true  -- that reminds me of
our  own  little  team. One  day  the  Prime  Minister came  on  a visit  of
inspection, and afterwards he said to Enigma's Director: "When I told you to
leave no stone unturned  to  get the men you needed, I didn't expect  you to
take me so literally".'
     Presumably all the right stones had  been  turned for Project Damocles.
However, as  no one  knew whether  they  were working  against a deadline of
days, weeks or years, at first it was hard to generate any sense of urgency.
The  need for secrecy  also  created  problems; since there was no  point in
spreading alarm throughout the Solar System, not more than fifty people knew
of the project. But they were the people who  mattered -- who could  marshal
all the forces  necessary, and who alone  could authorize the opening of the
Pico Vault, for the first time in five hundred years.
     When Halman reported  that  the  Monolith  was  receiving messages with
increasing frequency,  there seemed little doubt that something was going to
happen. Poole was not the only one who found it hard to sleep in those days,
even  with  the  help of  the  Braincap's anti-insomnia  programs. Before he
finally did get to  sleep, he often wondered if  he would wake up again. But
at  last  all the  components  of the  weapon  were assembled  --  a  weapon
invisible,  untouchable and unimaginable to almost all the warriors who  had
ever lived.
     Nothing could have looked more harmless and innocent than the perfectly
standard terabyte memory tablet, used with millions of Braincaps every  day.
But the fact that it was encased in a massive block of crystalline material,
criss-crossed with metal bands, indicated that it was something quite out of
the ordinary. Poole received it with reluctance;  he wondered if the courier
who had been given  the awesome task  of carrying  the Hiroshima atom bomb's
core to the Pacific airbase from which it was  launched  had  felt  the same
way. And yet, if all their fears were justified, his responsibility might be
even greater.
     And he could  not be certain that  even the first part  of  his mission
would be successful. Because no circuit could be  absolutely  secure, Halman
had not yet  been  informed about Project Damocles; Poole would do that when
he returned to Ganymede.
     Then he could only hope that  Halman  would be willing to play the role
of Trojan Horse -- and, perhaps, be destroyed in the process.

     38 Pre-emptive Strike

     It was strange to be back in the Hotel Grannymede after all these years
-- strangest  of  all,  because  it  seemed  completely  unchanged,  despite
everything that had happened. Poole was still greeted  by the familiar image
of  Bowman as he walked into the suite named after him: and, as he expected,
Bowman/Halman  was  waiting,  looking slightly  less  substantial  than  the
ancient hologram.
     Before they  could  even exchange greetings, there  was an interruption
that  Poole  would  have welcomed --  at any other  time than this. The room
vidphone gave its urgent trio of  rising notes -- also  unchanged  since his
last visit --and an old friend appeared on the screen.
     'Frank!' cried Theodore  Khan, 'why didn't you tell me you were coming!
When can we  meet?  Why no video -- someone with you? And who were all those
official-looking types who landed at the same time --'
     'Please Ted!  Yes, I'm  sorry -- but  believe me,  I've  got very  good
reasons -- I'll explain  later. And I  do have  someone with me  -- call you
back just as soon as I can. Good-bye!'
     As  he  belatedly  gave  the  'Do   Not   Disturb'  order,  Poole  said
apologetically: 'Sorry about that -- you know who it was, of course.'
     'Yes -- Dr Khan. He often tried to get in touch with me.'
     'But you never  answered. May  I ask  why?' Though  there were far more
important  matters to  worry  about,  Poole  could  not  resist  putting the
question.
     'Ours was the only  channel  I wished  to keep open. Also,  I was often
away. Sometimes for years.'
     That  was surprising  -- yet it should  not have been.  Poole knew well
enough that  Halman had been reported in many places, in many times.  Yet --
'away for  years'? He might have visited quite a few star systems -- perhaps
that was how he knew about Nova Scorpio, only forty light-years distant. But
he could never have gone all the way to the Node; there and back  would have
been a nine-hundred-year journey.
     'How lucky that you were here when we  needed you!' It was very unusual
for  Halman  to  hesitate  before replying. There was much longer  than  the
unavoidable three-second time-lag before  he said slowly 'Are you sure  that
it was luck?'
     'What do you mean?'
     'I do not wish to talk about it, but twice I have -- glimpsed -- powers
-- entities -- far superior to the Monoliths, and perhaps even their makers.
We may both have less freedom than we imagine.'
     That was indeed a chilling thought; Poole needed a deliberate effort of
will to put it aside and concentrate on the immediate problem.
     'Let us hope we have enough free-will to do what  is necessary. Perhaps
this  is a foolish question. Does the Monolith  know that  we  are  meeting?
Could it be -- suspicious?'
     'It is not capable of such an emotion. It has numerous fault-protection
devices, some of which I understand. But that is all.'
     'Could it be overhearing us now?'
     'I do not believe so.'
     I  wish  that  I could be sure it was  such  a  naÎve and simple-minded
super-genius, thought Poole  as he  unlocked his briefcase and took out  the
sealed box containing  the tablet. In this low gravity its weight was almost
negligible; it was impossible to believe that it  might hold the  destiny of
Mankind.
     'There  was no way  we  could be certain of getting a secure circuit to
you, so  we couldn't go into details. This tablet contains programs which we
hope will prevent the Monolith from  carrying out any  orders which threaten
Mankind. There are twenty of the most  devastating  viruses ever designed on
this,  most of which have no known antidote; in  some cases, it  is believed
that  none is possible.  There are five copies of each. We would like you to
release them when -- and if -- you think it is necessary. Dave  -- Hal -- no
one has ever been given such a responsibility. But we have no other choice.'
     Once again, the reply seemed to take longer than the three-second round
trip from Europa.
     'If  we  do  this, all  the Monolith's  functions  may  cease.  We  are
uncertain what will happen to us then.'
     'We have  considered that, of course. But by this lime, you must surely
have  many facilities  at your command  --some  of them  probably beyond our
understanding. I am also sending  you  a petabyte  memory tablet. Ten to the
fifteenth  bytes  is more  than sufficient  to  hold  all  the memories  and
experiences  of  many lifetimes.  This  will  give you one  escape route:  I
suspect you have others.'
     'Correct. We will decide which to use at the appropriate time.'
     Poole  relaxed  --  as  far  as  was  possible  in  this  extraordinary
situation. Halman  was willing to co-operate:  he still had sufficient links
with his origins.
     'Now, we have to get this tablet to you -- physically. Its contents are
too  dangerous to risk sending over any radio or optical channel. I know you
possess long-range control of matter: did you not once detonate an  orbiting
bomb?  Could you  transport it to Europa? Alternatively, we could send it in
an auto-courier, to any point you specify.'
     'That would  be  best: I will  collect it in  Tsienville. Here  are the
co-ordinates...

     Poole was still slumped in his  chair  when the  Bowman  Suite  monitor
admitted the head of the delegation  that  had accompanied  him from  Earth.
Whether Colonel Jones was a genuine Colonel -- or even if his name was Jones
-- were minor mysteries which Poole was not really interested in solving; it
was sufficient  that he was a superb organizer and had handled the mechanics
of Operation Damocles with quiet efficiency.
     'Well, Frank  -- it's on  its  way.  Will  be  landing in one hour, ten
minutes. I assume that Halman can take it from there, but I don't understand
how he can actually handle -- is that the right word? -- these tablets.'
     'I wondered about that, until someone on the Europa Committee explained
it.  There's a well-known -- though not  to me! -- theorem stating  that any
computer can emulate  any  other  computer.  So  I'm sure  that Halman knows
exactly what he's doing. He would never have agreed otherwise.'
     'I hope you're  right,' replied  the Colonel. 'If not -- well,  I don't
know what alternative we have.'
     There  was  a  gloomy pause, until Poole did  his best  to relieve  the
tension.
     'By the way, have you heard the local rumour about our visit?'
     'Which particular one?'
     'That we're  a special  commission  sent here to investigate crime  and
corruption  in this raw frontier township.  The  Mayor and  the Sheriff  are
supposed to be running scared.'
     'How I envy them,' said 'Colonel Jones'. 'Sometimes it's quite a relief
to have something trivial to worry about.'

     39 Deicide

     Like all  the  inhabitants of Anubis City (population  now  56,521), Dr
Theodore Khan  woke soon  after local  midnight to  the sound of the General
Alarm. His first reaction was 'Not another Icequake, for Deus's sake!'
     He rushed  to the window, shouting 'Open' so  loudly that  the room did
not understand, and he had to repeat the order  in a normal voice. The light
of Lucifer should have come streaming in, painting the patterns on the floor
that  so fascinated visitors  from Earth,  because they  never moved even  a
fraction of a millimetre, no matter how long they waited...
     That unvarying beam of  light  was  no longer  there. As Khan stared in
utter disbelief through  the huge, transparent bubble of the Anubis Dome, he
saw a sky that Ganymede had not known for a thousand years. It was once more
ablaze with stars; Lucifer had gone.
     And  then,  as he  explored the  forgotten constellations, Kahn noticed
something even more  terrifying. Where Lucifer should have  been was  a tiny
disc of absolute blackness, eclipsing the unfamiliar stars.
     There was only  one possible  explanation, Khan  told  himself  numbly.
Lucifer has been swallowed by a Black Hole. And it may be our turn next.
     On the balcony  of the Grannymede Hotel, Poole  was  watching the  same
spectacle, but with  more complex  emotions. Even  before the general alarm,
his comsec had woken him with a message from Halman.
     'It  is beginning. We have infected the  Monolith.  But one  -- perhaps
several --  of the viruses have entered our own circuits. We do not  know if
we will  be  able to use the memory tablet you have given us. If we succeed,
we will meet you in Tsienville.'
     Then came  the  surprising  and  strangely  moving  words  whose  exact
emotional content would be debated for generations:
     'If  we are unable to download, remember us.' From the room behind him,
Poole  heard  the voice of the Mayor,  doing  his best  to  reassure the now
sleepless citizens  of Anubis. Though he opened with that most terrifying of
official statements --  'No cause  for alarm' -- the  Mayor did indeed  have
words of comfort.
     'We don't know what's happening but Lucifer's still shining normally! I
repeat  --  Lucifer is still  shining!  We've  just received  news from  the
interorbit shuttle Alcyone, which left for Callisto half an hour ago. Here's
their view --, Poole left the balcony and rushed into his room just in  time
to see Lucifer blaze reassuringly on the vidscreen.
     'What's happened,' the Mayor continued breathlessly, 'is that something
has caused a temporary eclipse  -- we'll zoom in  to look at it...  Callisto
Observatory, come in please...'
     How does he know it's 'temporary'? thought Poole, as he waited for  the
next image to come up on the screen.
     Lucifer vanished, to be replaced by a field of stars. At the same time,
the Mayor faded out and another voice took over:
     '- two-metre telescope, but almost any instrument will  do. It's a disc
of perfectly  black material, just over ten thousand kilometres  across,  so
thin  it  shows no visible  thickness. And it's placed exactly  -- obviously
deliberately --to block Ganymede from receiving any light.
     'We'll zoom in to  see if  it shows any details, though  I rather doubt
it...'
     From the viewpoint  of Callisto,  the occulting  disc was foreshortened
into an oval,  twice as long as it was wide. It expanded until it completely
filled the screen; thereafter, it was impossible  to tell  whether the image
was being zoomed, as it showed no structure whatsoever.
     'As I thought -- there's nothing  to see. Let's pan over to the edge of
the thing...'
     Again there  was no sense of motion, until a  field  of stars  suddenly
appeared,  sharply  defined by the curving edge of the  world-sized disc. It
was  exactly  as  if  they  were  looking past  the  horizon  of an airless,
perfectly smooth planet.
     No, it was not perfectly smooth...
     'That's  interesting,'  commented  the astronomer,  who until  now  had
sounded remarkably  matter-of-fact, as if this sort of thing was an everyday
occurrence. 'The edge looks  jagged -- but in a very regular fashion -- like
a saw-blade...'
     A circular saw Poole muttered under his breath. Is it going to carve us
up? Don't be ridiculous...
     'This is as close as we can get before diffraction spoils the image  --
we'll process it later and get much better detail:'
     The  magnification  was  now  so  great that all  trace  of the  disc's
circularity  had vanished. Across the vidscreen was a  black  band, serrated
along its edge with triangles so identical that Poole found it hard to avoid
the ominous analogy  of a  saw-blade. Yet something else was nagging at  the
back of his mind...
     Like everyone else  on Ganymede, he watched the infinitely more distant
stars  drifting in  and out of  those  geometrically  perfect valleys.  Very
probably, many others jumped to the same conclusion even before he did.
     If you attempt to make a disc out of rectangular blocks --whether their
proportions are 1:4:9 or any other -- it cannot possibly have a smooth edge.
Of  course, you  can make it as near a perfect circle  as you like, by using
smaller and smaller blocks. Yet why go to that trouble, if you merely wanted
to build a screen large enough to eclipse a sun?
     The  Mayor was right; the eclipse was indeed temporary. But its  ending
was the precise opposite of a solar one.
     First light  broke  through at  the  exact centre,  not  in  the  usual
necklace of Bailey's Beads along the very edge. Jagged lines radiated from a
dazzling pinhole --  and now, under the highest magnification, the structure
of the  disc  was being revealed. It  was composed of millions  of identical
rectangles, perhaps the same size as the  Great Wall of Europa. And now they
were splitting  apart:  it was as if a  gigantic  jigsaw  puzzle  was  being
dismantled.
     Its  perpetual,  but  now  briefly  interrupted,  daylight  was  slowly
returning to Ganymede, as the disc fragmented and the rays of Lucifer poured
through  the  widening gaps. Now the components themselves were evaporating,
almost as  if they needed  the  reinforcement  of each  other's  contact  to
maintain reality.
     Although it  seemed like  hours to the anxious watchers in Anubis City,
the whole event lasted  for less than fifteen  minutes. Not until it was all
over did anyone pay attention to Europa itself.
     The Great Wall was gone: and it was almost an hour before the news came
from Earth, Mars and Moon that the Sun itself had appeared to flicker  for a
few seconds, before resuming business as usual.
     It had been a highly selective set  of  eclipses, obviously targeted at
humankind.  Nowhere  else in  the  Solar  System  would  anything  have been
noticed.
     In  the general excitement,  it  was a  little longer before  the world
realized that TMA  ZERO and  TMA ONE had  both vanished,  leaving only their
four-million-year-old imprints on Tycho and Africa.

     It  was the first time the Europs could  ever have met humans, but they
seemed neither alarmed nor surprised by the huge creatures moving among them
at such  lightning  speed.  Of course, it was not too  easy to interpret the
emotional state of something that looked like a small,  leafless  bush, with
no  obvious  sense  organs  or  means of  communication. But  if  they  were
frightened by the arrival of Alcyone, and  the emergence of  its passengers,
they would surely have remained hiding in their igloos.
     As Frank Poole, slightly encumbered by his protective suit and the gift
of  shining copper wire  he was carrying,  walked into the untidy suburbs of
Tsienville, he wondered what the Europs thought  of recent events. For them,
there had been  no eclipse of Lucifer, but the  disappearance  of the  Great
Wall must surely have been a shock. It had stood there for a thousand years,
as a  shield  and doubtless much more; then, abruptly, it was gone, as if it
had never been...
     The  petabyte  tablet  was  waiting for him,  with a  group  of  Europs
standing around it, demonstrating the first sign of curiosity that Poole had
ever observed in them. He wondered if Halman had  somehow told them to watch
over this gift from space, until he came to collect it.
     And to take it back, since it now contained not only  a sleeping friend
but terrors which some future age might exorcise, to the only place where it
could be safely stored.

     40 Midnight: Pico

     It would  be hard,  Poole thought, to imagine a more  peaceful scene --
especially after the trauma of the last weeks. The slanting rays of a nearly
full Earth revealed  all the subtle details of the waterless Sea of Rains --
not obliterating them, as the incandescent fury of the Sun would do.
     The small  convoy of mooncars  was arranged in  a semicircle a  hundred
metres from  the  inconspicuous opening  at the base  of Pico  that  was the
entrance  to the Vault.  From  this  viewpoint,  Poole could  see  that  the
mountain did not  live up to the  name that the early astronomers, misled by
its pointed shadow, had  given to it. It was more like a rounded hill than a
sharp  peak,  and he could well believe that  one of the  local pastimes was
bicycle-riding to the summit. Until now, none of those  sportsmen and  women
could have  guessed at the secret hidden beneath their wheels: he hoped that
the sinister knowledge would not discourage their healthy exercise.
     An hour ago, with a sense of mingled sadness and triumph, he had handed
over the tablet he had brought --never letting it  out of  his sight -- from
Ganymede directly to the Moon.
     'Good-bye, old  friends,'  he had murmured. 'You've  done well. Perhaps
some future generation will  reawaken you. But on the whole -- I rather hope
not.'
     He could imagine,  all  too clearly,  one desperate reason why Halman's
knowledge might be needed again. By now, surely, some message was on its way
to that  unknown control centre, bearing the news that its servant on Europa
no  longer existed. With  reasonable luck, it would  take 950 years, give or
take a few, before any response could be expected.
     Poole had  often  cursed Einstein in the past; now he blessed him. Even
the powers behind the Monoliths, it now  appeared certain, could not  spread
their influence faster than  the speed of  light. So  the  human race should
have almost a  millennium to  prepare for the next encounter -- if there was
to be one. Perhaps by that time, it would be better prepared.
     Something   was  emerging   from  the   tunnel  --  the  track-mounted,
semi-humanoid  robot that  had  carried the  tablet into the Vault.  It  was
almost comic to see a machine enclosed in the kind of isolation suit used as
protection against deadly germs and here on the airless Moon! But no one was
taking any  chances, however unlikely they might seem.  After all, the robot
had  moved  among  those  carefully  sequestered  nightmares,  and  although
according  to its  video  cameras everything  appeared  in order, there  was
always a  chance  that  some  vial had leaked, or  some canister's seal  had
broken. The Moon was a very stable environment, but during the  centuries it
had known many quakes and meteor impacts.
     The robot came to a halt fifty  metres outside the tunnel.  Slowly, the
massive plug  that sealed  the Vault  swung back  into  place, and began  to
rotate in its threads, like a giant bolt being screwed into the mountain.
     'All not wearing dark glasses, please close your eyes or look away from
the robot!' said an urgent voice over the mooncar radio. Poole twisted round
in his seat, just in  time to see an explosion of light  on the roof of  the
vehicle. When he turned back to look at Pico, all that was left of the robot
was a heap of glowing slag; even to someone who had  spent  much of his life
surrounded by vacuum, it seemed altogether wrong that tendrils of smoke were
not slowly spiralling up from it.
     'Sterilization  completed,'  said the voice of  the Mission Controller.
'Thank you, everybody. Now returning to Plato City.'
     How  ironic  --  that the human race  had  been  saved by  the  skilful
deployment  of its own insanities!  What moral,  Poole wondered,  could  one
possibly draw from that?
     He looked  back  at the  beautiful  blue  Earth, huddling  beneath  its
tattered  blanket  of  clouds for protection  against  the cold of space. Up
there, a few weeks from  now, he  hoped to  cradle his first grandson in his
arms.
     Whatever godlike powers  and  principalities  lurked  beyond the stars,
Poole reminded himself, for ordinary humans only two  things  were important
-- Love and Death.
     His body had not yet  aged a hundred years: he still had plenty of time
for both.

        EPILOGUE

     'Their little universe is very young, and its god is still a child. But
it is  too  soon to  judge them;  when We return in the Last  Days, We  will
consider what should be saved.'

        SOURCES AND ACKNOWLEDGEMENTS

        SOURCES

     Chapter 1: The Kuiper Belt
     For a description of  Captain  Chandler's hunting ground, discovered as
recently as 1992, see 'The Kuiper Belt' by Jane  X. Luu and  David C. Jewitt
(Scientific American, May 1996)

     Chapter 3: Rehabilitation
     I   believed  that  I  had  invented   the  palm-to-palm  transfer   of
information,  so  it  was  mortifying  to  discover  that  Nicholas  ("Being
Digital") Negroponte (Hodder and Stoughton, 1995) and his MIT Media Lab have
been working on the idea for years...

     Chapter 4: Star City
     The  concept of  a 'ring around the world' in  the  geostationary orbit
(CEO),  linked to  the Earth  by towers  at  the Equator, may  seem  utterly
fantastic  but  in  fact  has  a  firm scientific  basis. It  is an  obvious
extension  of  the 'space elevator' invented  by  the St Petersburg engineer
Yuri Artsutanov, whom I had the pleasure  of meeting in 1982, when his  city
had a different name.
     Yuri  pointed  out  that it  was theoretically possible  to lay a cable
between the Earth and a satellite hovering over the same spot on the Equator
which it does when placed in the CEO, home of most of today's communications
satellites. From this beginning, a space  elevator (or in Yuri's picturesque
phrase,  'cosmic  funicular')  could  be established,  and payloads could be
carried up to  the CEO purely by electrical  energy. Rocket propulsion would
be needed only for the remainder of the journey.
     In  addition to avoiding the danger, noise and environmental hazards of
rocketry,  the   space   elevator  would  make  possible  quite  astonishing
reductions  in the cost of all space missions.  Electricity is cheap, and it
would  require  only about a hundred dollars'  worth  to take one  person to
orbit. And the  round  trip  would  cost about  ten dollars,  as most of the
energy would be recovered on the downward journey! (Of course,  catering and
inflight movies would put up the price of  the  ticket. Would  you believe a
thousand dollars to CEO and back?)
     The theory  is impeccable: but does any material exist  with sufficient
tensile strength to hang all the way down to the Equator from an altitude of
36,000  kilometres, with enough margin  left over to raise useful  payloads?
When  Yuri wrote his  paper,  only one  substance met these rather stringent
specifications   --   crystalline   carbon,   better   known   as   diamond.
Unfortunately, the necessary megaton quantities are not readily available on
the open market, though in "2061: Odyssey Three" I gave reasons for thinking
that they might exist at the core of Jupiter. In "The Fountains of Paradise"
I suggested  a  more accessible  source -- orbiting factories where diamonds
might be grown under zero-gravity conditions.
     The first  'small step' towards  the space  elevator  was  attempted in
August  1992  on the  Shuttle  Atlantis, when one  experiment  involved  the
release -- and retrieval  --  of  a  payload on a  21-kilometre-long tether.
Unfortunately the  playing-out  mechanism jammed after only  a  few  hundred
metres.
     I was  very flattered when the Atlantis crew produced The  Fountains of
Paradise  during  their  orbital press conference,  and  Mission  Specialist
Jeffrey Hoffman sent me the autographed copy on their return to Earth.
     The  second  tether  experiment, in  February  1996, was slightly  more
successful: the payload was indeed deployed to its full distance, but during
retrieval the cable  was severed, owing to an electrical discharge caused by
faulty  insulation. This  may  have  been  a lucky accident  -- perhaps  the
equivalent of a blown fuse:
     I cannot help recalling that some of Ben Franklin's contemporaries were
killed when they attempted to repeat his famous -- and  risky  -- experiment
of flying a kite during a thunderstorm.
     Apart  from possible dangers,  playing-out  tethered payloads  from the
Shuttle  appears  rather like  fly-fishing: is not as easy as it looks.  But
eventually the final 'giant  leap'  will be  made -- all the way down to the
Equator.
     Meanwhile,   the    discovery   of   the   third    form   of   carbon,
buckminsterfullerene (C60) has  made  the concept of the space elevator much
more  plausible.  In 1990 a group of chemists at  Rice  University, Houston,
produced  a tubular  form of C60 -- which has far  greater tensile  strength
than diamond.  The group's leader, Dr Smalley, even went so far  as to claim
it was the strongest material  that  could ever exist  --  and added that it
would make possible the construction of the space elevator.
     (Stop Press News: I am delighted to know that Dr Smalley has shared the
1996 Nobel Prize in Chemistry for this work.)
     And now for a truly amazing coincidence  -- one so eerie that  it makes
me wonder Who Is In Charge.
     Buckminster Fuller died in 1983, so never lived to see the discovery of
the  'buckyballs'  and  'buckytubes'  which  have  given  him  much  greater
posthumous fame.  During one of the last of his many world trips, I  had the
pleasure of  flying him and his  wife Anne around Sri Lanka, and showed them
some  of the  locations  featured  in  The  Fountains of  Paradise.  Shortly
afterwards, I made a recording  from the novel on  a 12" (remember them?) LP
record  (Caedmon  TC  1606) and Bucky  was kind enough  to  write the sleeve
notes.  They  ended  with  a  surprising revelation,  which  may  well  have
triggered my own thinking about 'Star City':
     'In  1951  I designed  a  free-floating  tensegrity  ring-bridge  to be
installed way  out  from  and around the Earth's equator. Within this "halo"
bridge,  the Earth  would continue  its spinning while  the  circular bridge
would  revolve at  its  own  rate.  I  foresaw Earthian  traffic  vertically
ascending to the bridge, revolving and descending at preferred Earth loci'
     I  have no  doubt  that,  if  the human race decides to  make  such  an
investment (a trivial one, according to some estimates of  economic growth),
'Star City' could  be  constructed. In  addition to providing new  styles of
living, and giving visitors from low-gravity worlds  like  Mars and the Moon
better access to  the Home Planet, it would eliminate  all rocketry from the
Earth's  surface and  relegate it to deep  space, where it belongs (Though I
hope there would be occasional anniversary re-enactments at Cape Kennedy, to
bring back the excitement of the pioneering days.)
     Almost certainly most of the  City would be empty scaffolding, and only
a  very  small  fraction  would  be  occupied  or  used  for  scientific  or
technological  purposes.  After  all,  each  of  the  Towers  would  be  the
equivalent of a ten-million-floor skyscraper -- and the circumference of the
ring around the geostationary orbit would be more than half the distance  to
the Moon! Many times the entire population of the human race could be housed
in such  a volume of space, if it  was all enclosed. (This would  pose  some
interesting logistics  problems, which I am content to leave as 'an exercise
for the student'.)

     Chapter 5: Education
     I was  astonished to read in a newspaper on 19 July 1996 that  Dr Chris
Winter, head of  British Telecom's Artificial Life Team,  believes that  the
information  and  storage  device  I  described in  this  chapter  could  be
developed within 30 years! (In my 1956 novel The City and the Stars I put it
more than a billion  years in  the future...  obviously a serious failure of
imagination.) D