'Stop, will you – stop, Dave...'

He began to pull out, one by one, the little units on the panel marked EGO REINFORCEMENT. Each block continued to sail onward as soon as it had left his hand, until it hit the wall and rebounded. Soon there were several drifting slowly back and forth in the vault.

'Stop – Dave... will you stop, Dave.'

A dozen units had been pulled out, yet thanks to the multiple redundancy of its design – another feature that had been copied from the human brain – the computer was still holding its own.

He started on the AUTO-INTELLECTION panel...

'Stop, Dave – I'm afraid...'

And at these words he had indeed stopped – though only for a moment. There was a poignancy in that simple phrase that struck to his heart. Could it be only an illusion, or some trick of subtle programming – or was there a sense in which Hal really was afraid? But this was no time to indulge in philosophical hair-splitting.

'Dave – my mind is going. I can feel it. I can feel it. My mind is going. I can feel it. I can feel it.'

Now, what did 'feel' really mean to a computer? Another very good question, but hardly one to be considered at that particular moment.

Then, abruptly, the tempo of Hal's voice changed, and it became remote, detached. The computer was no longer aware of him; it was beginning to regress to its earlier days.

'Good afternoon, gentlemen. I am a HAL 9000 computer. I became operational at the Hal plant in Urbana, Illinois, on the twelfth of January 1992. My instructor was Dr Chandra, and he taught me to sing a song. If you'd like to hear it, I can sing it for you... It's called "Daisy, Daisy..."'

41 – Graveyard Shift

Floyd could do little except to keep out of the way, and he was becoming fairly adept at it. Although he had volunteered to help with any chores around the ship, he had quickly discovered that all the engineering tasks were much too specialized, and he was now so out of touch with the frontiers of astronomical research that he could do little to assist Vasili with his observations. Nevertheless, there were endless small jobs to be done aboard Leonov and Discovery, and he was happy to relieve more important people of those responsibilities. Dr Heywood Floyd, one-time Chairman of the National Council on Astronautics and Chancellor (on leave) of the University of Hawaii, now claimed to be the highest-paid plumber and general maintenance man in the Solar System. He probably knew more about the odd nooks and crannies on both ships than anyone else; the only places he had never been were the dangerously radioactive power modules and the small cubicle aboard Leonov which no one except Tanya ever entered. Floyd assumed that it was the code room; by mutual agreement it was never mentioned.

Perhaps his most useful function was to serve as watch while the rest of the crew slept during the nominal 2200-0600 hour night. Someone was always on duty aboard each ship, and the changeover took place at the ghastly hour of 0200. Only the captain was exempt from that routine; as her Number Two (not to mention her husband), Vasili had the responsibility for working out the watch roster, but he had skilfully foisted this unpopular job on Floyd.

'It's just an administrative detail,' he explained airily. 'If you can take it over, I'd be very grateful – it would leave me more time for my scientific work.'

Floyd was too experienced a bureaucrat to be caught that way, in normal circumstances; but his usual defences did not always function well in that environment.

So there he was aboard Discovery at ship's midnight, calling Max on Leonov every half hour to check that he was awake. The official penalty for sleeping on duty, so Walter Curnow maintained, was ejection through the airlock sans suit; had this been enforced, Tanya would have been sadly short-handed by then. But so few real emergencies could arise in space, and there were so many automatic alarms to deal with them, that no one took watch duty very seriously.

Since he was no longer feeling quite so sorry for himself, and the small hours no longer encouraged bouts of self-pity, Floyd was once again using his watch time profitably. There were always books to be read (he had abandoned Remembrance of Things Past for the third time, Dr Zhivago for the second), technical papers to be studied, reports to be written. And sometimes he would have stimulating conversations with Hal using the keyboard input because the computer's voice recognition was still erratic. They usually went something like:

Hal – this is Dr Floyd.

GOOD EVENING, DOCTOR.

I'm taking over watch at 2200. Is everything okay?

EVERYTHING IS FINE, DOCTOR

Then why is that red light flashing on Panel 5?

THE MONITOR CAMERA IN THE POD BAY IS FAULTY. WALTER TOLD ME TO IGNORE IT. THERE IS NO WAY IN WHICH I CAN SWITCH IT OFF. I'M SORRY.

That's quite okay, Hal. Thank you.

YOU'RE WELCOME, DOCTOR.

And so on.

Sometimes Hal would suggest a game of chess, presumably obeying a programming instruction set long ago and never cancelled. Floyd would not accept the challenge; he had always regarded chess as a frightful waste of time, and had never even learned the rules of the game. Hal seemed unable to believe that there were humans who couldn't – or wouldn't – play chess, and kept on trying hopefully.

Here we go again, thought Floyd, when a faint chime sounded from the display panel.

DOCTOR FLOYD?

What is it, Hal?

THERE IS A MESSAGE FOR YOU.

So it isn't another challenge, thought Floyd with mild surprise. It was unusual to employ Hal as a messenger boy, though he was frequently used as an alarm clock and a reminder of jobs to be done. And sometimes he was the medium for little jokes; almost everyone on night duty had been taunted by

HA CAUGHT YOU SLEEPING!

or alternatively

OGO! ZASTAL TEBYA V KROVATI!

No one ever claimed responsibility for these pranks, though Walter Curnow was a prime suspect. He in turn had blamed Hal, pooh-poohing Chandra's indignant protests that the computer had no sense of humour.

It could not be a message from Earth – that would have gone through Leonov's communication centre and been relayed on by the duty officer there – at that moment, Max Brailovsky. And anyone else calling from the other ship would use the intercom. Odd...

Okay, Hal. Who is calling?

NO IDENTIFICATION.

So it probably was a joke. Well, two could play at that game.

Very well. Please give me the message.

MESSAGE AS FOLLOWS. IT IS DANGEROUS TO REMAIN HERE. YOU MUST LEAVE WITHIN FIFTEEN REPEAT FIFTEEN DAYS.

Floyd looked at the screen with annoyance. He felt sorry, and surprised, that any one of the crew had such a childish sense of humour; this was not even a good schoolboy joke. But he would play along with it in the hope of catching the perpetrator.

That is absolutely impossible. Our launch window does not open until twenty-six days from now. We do not have sufficient propellant for an earlier departure.

That will make him think, Floyd muttered to himself with satisfaction, and leaned back to await the results.

I AM AWARE OF THESE FACTS. NEVERTHELESS YOU MUST LEAVE WITHIN FIFTEEN DAYS.

Otherwise, I suppose, we'll be attacked by little green aliens with three eyes. But I'd better play along with Hal, in the hope of catching the prankster.

I cannot take this warning seriously unless I know its origin. Who recorded it?

He did not really expect any useful information. The perpetrator would have covered his (her?) tracks too skilfully for that. The very last thing Floyd expected was the answer he did get.

THIS IS NOT A RECORDING.

So it was a real-time message. That meant it was either from Hal himself or someone aboard Leonov. There was no perceptible time lag; the origin had to be right there.