Less than half a kilometre, and closing on it.

How fast?

I don't know. Wait.

There was a long silence except for the hum.

'He's getting some trouble here. He's either picking up a stray bleep from a different sensor field, or the computer's asking for more data.'

The other technician, a man with a humped back and grey smoked glasses, said to nobody: 'We're not sure whether they've got a Magnetic Anomaly Detector.'

'If they have,' the CIA man said, 'they got it from us.' I thought it was meant to be a joke but no one laughed.

All right. All right. It's now 760 metres from your No. 4 battery. Course is now 121°, position 17-F.

It's isolated?

Yes. I have a kill ready.

Silence again.

The ambassador moved heavily to the door and went out. No one looked anywhere but at the tape-deck.

Confirm you have a kill ready.

I confirm.

Other sounds came in now, with voices in the distant background.

Keep me advised.

Something like a minute went by and there was nothing we could hear that told us anything. Croder glanced across at the CIA chief, who was sitting with his elbows on the desk and his face between his fists, stretching the skin into furrows. He was watching the tape-deck; he didn't catch Croder's glance.

I didn't know the figures involved in that area: the depth or salinity or current or the cruise speed of a torpedo.

Advise me. Did I make a hit? Did I make a hit?

The voice was excited now.

Wait.

Croder took out his cigarette-case and lit one of those black-tipped things he smoked, but he didn't look away from the tape-deck.

No. You did not make a hit.

Advise me.

Wait.

The hump-backed technician drew in his breath suddenly and turned to Croder. 'Can I have one of those?'

He lit up and turned away from the desk, so as not to watch the tape-deck.

New position: 17-G on the east grid. 540 metres from your No. 4 battery. Profile is broadside on. You have a kill.

Keep me advised.

We had to wait again. The CIA man had closed his eyes now, his fists kneading his face into a loose mask. Croder glanced towards the door and away again. The silence drew out.

Advise me. Did we make a hit? Did we make a hit?

The grid hummed. There were other sounds, vague and intermittent, and a quick beeping began. It lasted a minute, maybe more.

The hump-back had turned round to watch the tape-deck.

Confirm. You made a hit. I repeat: You made a hit.

The thin technician used his handkerchief again.

'We made modifications to this model so we could extract parameters from the speech waveform. That gives us a better speech recognition performance. What's happening is that the variable electronic filter is moving to higher and higher frequencies while the stylus is moving parallel to the axis of the drum. What we're getting from this pattern are the dimensions of time, frequency and amplification.'

The voice was almost continuous on this second tape..No. 5 sonobuoy responding. Object at 43-A. Speed of movement constant. Approach to No. 6 sonobuoy at steady 68 degrees with appropriate response. Transducers running in No. 1 bay.

Tape gap.

All configurations are normal. Bathythermograph average is 42°. Total east grid surveillance is now ten buoys.

Tape gap.

I'm now triangulating on S-35. It's 12-B on the east grid, course 76°. Depth now 70 metres.

'S-35 is one of their diesel subs,' the technician with the cold said. He let the tape run on for another two or three minutes and then the CIA chief asked him to shut it down. He took his face out of his hands and got up and went out of the room, coming back with the ambassador.

'So tell us,' he said to the technicians.

The hump-back prodded his cigarette out. 'All we can say for sure is that the voice on the second tape is the same as the one on the first tape that was doing the advising. He's one of their sonar operators. The other man of course was in charge of a torpedo battery.'

The CIA chief dug his hands into his pockets, putting his head back, speaking to the ceiling. 'That was the actual attack on the Cetacea we were listening to? The actual sinking?'

'Yes.'

'Bastards. Bastards'

No one broke the silence for a while. It was a silence for the one hundred and five crew of the SSN Cetacea, missing on patrol.

Croder said quietly to the technicians: 'What you're saying, then, is that the voice of the man advising is genuine — a genuine naval officer working the sonar unit.'

'Right. Look at this spectrogram. Identical patterns in every single speech mode. Same man.'

'And from this we can assume,' the CIA chief said in a flat tone, 'that the tape you people just brought back from Murmansk is a genuine recording of the incident. Is that right?'

'Not quite,' Croder said. 'On the face of it, we don't really doubt that it's genuine. This is because our agent in Murmansk has been installed there as a sleeper for nearly five years, and has been sending back the most valuable material. He realized the enormous significance of this particular run of tape, and had it duplicated. He then signalled us and told us he was sending it by courier.'

I watched the two technicians for a moment. They weren't just boffins: they must have been security-screened on the highest level.

'We know, of course, that the Soviets will deny the whole thing and say that we've faked this tape ourselves. Our answer to that is that the voice on the recent tape tallies precisely with one of the voices the CIA has been recording as a routine acoustic surveillance operation for a very long time. There's a second point. If anyone — meaning, I don't doubt, the Soviets — faked this tape and deliberately allowed us to get hold of it, then we can say with absolute certainty that they had to persuade or order an actual naval officer to speak on that new tape, acting out the despatch of those torpedoes. They-'

'Why in hell would they want to do that?' Ambassador Morrison asked him.

Croder spread his hands open. His smile was almost apologetic. 'I've no wish to complicate things, Mr Ambassador. It's simply that we want to have every answer ready.'

'We're talking about Russian double think,' the CIA chief nodded.

'It's that convoluted?'

'Not really,' Croder said. 'What I'm saying now is that if, for example, the Soviets wished to scuttle the proposed summit conference for whatever obscure reason, they couldn't do it more simply than by faking this tape and allowing us to come by it.'

'You believe that's what they did?'

'I believe it's most unlikely. We're just covering the contingency. Most unlikely of all is the idea that a naval officer could lend himself to the deceit, however threatened or cajoled or bribed with honours and promotion.'

The ambassador watched Croder with his large head lowered and his eyes level. 'Then you believe this tape is genuine, and that it gives us irrefutable evidence that the Soviets in fact ordered the attack and sinking of the submarine. Is that correct?'

A faint apologetic smile. 'Not quite. I don't believe in the least that the Soviets — by which you mean the Soviet authorities — ordered the attack on the Cetacea. I believe that when she was discovered either close to the twelve-mile limit or actually within Soviet waters, the officer in command of No. 4 torpedo battery made the attack and sank the boat.'

'Without getting permission?'

'Yes.'

'Why?'

'For one of several understandable reasons. He's young, keen, ambitious, perhaps. What a bone to bring to the mat of his superiors! The hero of the hour, destroying in the nick of time an American nuclear submarine in the act of spying on the Soviets' most important naval base — the gateway to the Atlantic, bristling with the most highly secret technology.'