'Each pod can be opened and closed individually,' she explained. 'Getting in is easy, although you might be soaked on your first attempt. The water is heated on its way into the basin so it's a balmy fifteen degrees, but don't think of taking off your suits. If you were tipped into the ocean without one, it would all be over in minutes. The water temperature off the coast of Greenland reaches a maximum of two degrees.'

'Any questions?' Roscovitz organised the first groups, pairing scientists with pilots. 'Let's go, then. We'll stick close to the vessel. Our friendly colleagues from the dolphin fleet have given us the all-clear, but things could change at any moment. Leon, you're coming with me. We'll take Deepflight 1.'

He jumped on to the boat, which lurched from side to side. Anawak tried to copy him, but lost his balance and landed in the water. He spluttered to the surface and was greeted by laughter.

'I guess that's what I meant,' Browning said drily.

Anawak pulled himself on to the hull and slid into the pod on his belly. To his surprise it felt comfortable and roomy. He wasn't lying completely flat; the pod slanted upwards, so his body assumed the position of a ski jumper in mid-flight. In front of him he found a control panel. Roscovitz switched on the power, and the pods closed soundlessly.

'Not exactly the Ritz, eh, Leon?'

The commander voice boomed out of the loudspeakers and into Anawak's ears. He turned his head. A metre away from him, Roscovitz was looking out of his acrylic pod and grinning at him. 'See that joystick in front of you? Remember I told you it's like a plane? Well, that's how it flies. So you're going to have to learn to fly it like a plane – gaining and losing height, banking round. You need to be able to move in all four directions. It's equipped with four thrusters that generate sufficient counter-force to allow the vehicle to hover. I'll fly the first loop, then you'll take over, at which point I'll tell you what you're doing wrong.'

All of a sudden the vessel tipped forward. Water washed over the acrylic domes, and they banked down in a gentle curve. Floodlights lit up at the bow and on the wings. Anawak saw the planks at the bottom of the basin slide beneath them, and then they were hovering at the opening to the sluice. The flaps opened to reveal a shaft that stretched down several metres, fully lit, with a dark steel hatch at the bottom. The Deepflight sank leisurely through it and the glass flaps closed above them. He felt a wave of queasiness.

'Don't worry,' said Roscovitz. 'They'll let us out pretty quickly. It's coming back in that takes time.'

The steel flaps juddered into motion. As the enormous metal panels moved apart, the view opened up to show the dark, featureless expanse of the depths. The Deepflight sank into the unknown.

Roscovitz accelerated and banked round. The boat turned onto its side. Anawak was enthralled. He'd driven conventional submersibles designed for use in the upper layers of the ocean, but this was different. The Deepflight handled the water like a sports plane. And it was fast! In a car, fourteen miles per hour- the equivalent of twelve knots – would seem slow, but underwater the Deepflight was displaying an amazing burst of speed. He watched in fascination as they emerged from beneath the Independence and the rippling surface of the water came into view overhead. Roscovitz dipped the nose of the submersible at a precipitous angle. He banked round again, headed towards the stern of the helicopter-carrier and dived back under. Above them, the enormous rudder blade of the vessel whizzed by.

Then Roscovitz banked sharply. Anawak kept expecting to see the round black-and-white face of an orca appear before them, but instead two dolphins peered in. With cameras on their heads, they pranced jauntily around the submersible.

'Smile, Leon!' laughed Roscovitz. 'You're on camera!'

Then a light flashed on. 'You're taking over,' said Roscovitz. 'If anything comes along and tries to eat us, we'll give it a brace of torpedoes for breakfast. But I'll take care of that. You focus on steering.'

Anawak was momentarily flummoxed. His grip on the joystick tightened. Roscovitz hadn't told him what to do, so he headed straight on.

'Hey, Leon, no snoozing at the wheel. I've been on bus journeys that were more exciting than this.'

'What do you want me to do?'

'Anything. Fly us to the moon!'

The moon in this scenario must be below us, thought Anawak. Here goes.

He thrust the joystick forward.

The Deepflight's nose jerked down and they headed into the depths. Anawak stared into the darkness. He pulled the joystick towards him, this time more gently. The boat straightened. He tried a curve, but turned too sharply. He tried another. He knew he was steering too jerkily, but really it was easy. It was all a question of practice.

Ahead he spotted a second Deepflight. Suddenly he started to enjoy himself He could have carried on for hours.

'Not bad, Leon. I reckon your technique's enough to make anyone travel-sick, but that's nothing we can't fix. Now put her on the horizontal. Excellent. That's it, drift along slowly. Now let's have a go at operating the articulated arms. There's nothing to it.'

After five minutes Roscovitz took over the controls and guided the boat slowly into the shaft. There was an agonising minute inside the sluice, but then the glass flaps opened and they surfaced. Anawak wasn't sorry to be back: the early-morning visit from the orcas had unnerved him. And there were all the other surprises that the sea might spring on an unsuspecting pilot.

Roscovitz opened the pods, they lifted themselves out of the boat and jumped on to the jetty.

Floyd Anderson was waiting for them. 'How was it?' he asked. He didn't seem to care.

'Fun.'

'Well, folks, the party's over.' The first officer watched the second boat surface. 'As soon as you guys stick your heads under water, stuff happens. We've picked up a signal.'

'What?' Crowe joined them. 'What kind?'

'We were hoping you could tell us.' Anderson stared straight past her. 'It's loud, and it's coming from somewhere nearby.'

COMBAT INFORMATION CENTER

'A low-frequency signal,' said Shankar. 'Same pattern as Scratch.'

Shankar and Crowe had rushed to the CIC. In the meantime they'd received confirmation from the onshore station. According to their calculations, the noise was coming from the vicinity of the Independence.

Li walked in. 'Can you make any sense of it?'

'Not right away.' Crowe shook her head. 'We'll need some help from the computer. We'll get it to break down the signal and start looking for patterns.'

'Call me some time next year.'

'Is there a problem?' Shankar growled.

'I was just wondering how you intended to decipher it in a viable timescale, when your guys at NOAA have been puzzling over Scratch for years.'

'And you're asking that now?

'Come on, children.' Crowe scrabbled around for her cigarettes and lit up. 'I keep telling you that communicating with an alien species is an entirely different matter. Yesterday's signal was probably the first human message that the yrr have been able to decode. They'll reply in a similar format.'

'You really think they'll use the same coding?'

'Well, if the yrr exist, if this is a message, if they understood our code, and if they're interested in talking to us – then, yes, I do.'

'Why are they using the infrasound spectrum and not a frequency we can hear?'

'Why shouldn't they use infrasound?' Crowe asked, surprised.

'You'd think it would be diplomatic.'

'If a Russian were to address you in bad English, would you reply to him in Russian?'