'It gets heavier.'

'Indeed. So, the water gets heavier, which makes it start to sink. Surface currents turn into deep-water currents, or even bottom-water currents, and the flow direction changes. It's exactly the same the other way round, but the water goes upwards, from cold to warm. That way, all the major currents are continuously in motion. And because they're all interconnected, there's a constant process of exchange.'

The float was lowered to the surface of the water. Bauer hurried to the railings and leaned over, gesturing impatiently for Weaver to follow. 'What are you waiting for? Come on, you'll get a better view from here.'

She stood next to him. Eyes glowing, Bauer was gazing out to sea. 'Imagine if there were floats in every single current!' he said. 'Just think how much we'd learn.'

'What are the glass spheres for?'

'They keep the float suspended in the current. There are weights at the other end too, but the key to the whole thing is the cylinder in the middle. All the equipment is in there. Electronic controls, microprocessor, power supply. And it's neutrally buoyant. Isn't that amazing? Neutrally buoyant!'

'I'd find it even more amazing if you told me what that meant.'

'Oh, yes. Of course…' Bauer tugged as his beard. 'Well, we had to think about how we could get the floats to- You see, it's like this: fluids are practically incompressible. That is to say, you can't compress them any further. Water is the key exception. You can't, er, squish it much, but it's possible. So that's what we do. We compress the water in the cylinder so there's always the same amount in there, but sometimes it's heavier and sometimes it's lighter. So the weight of the float can be varied without changing the volume.'

'Ingenious.'

'It certainly is! It can even be programmed to do it by itself – compressing, decompressing, compressing, decompressing, sinking down and rising up – without us lifting a finger. Clever, don't you think?'

Weaver watched the tube sink into the sea.

'It means the float can travel independently for months and even years, transmitting radio signals, while we track it and reconstruct the speed and the movement of the current. Off it goes.'

The drifting profiler had vanished.

'And where's it heading now?'

'That's the question.'

Weaver looked at him intently.

Bauer sighed resignedly. 'I know, I know. You want to hear about my work. Goodness me, you're tenacious… Very well, we can talk in the lab. But the findings are unsettling, to say the least.'

'People love to be unsettled. Haven't you heard? Jellyfish invasions, scientific anomalies, people going missing and sinking ships. You'll be in good company.'

'Do you think so?' Bauer shook his head. 'You're probably right. I'll never understand what publicity's about. I'm only a scientist.'

CONTINENTAL MARGIN, Norwegian Sea

'Shit,' Stone groaned. 'It's a blow-out.'

On board the Sonne, everyone in the control room stared at the screen. All hell seemed to have broken loose on the seabed.

Bohrmann spoke into the microphone: 'We've got to get out of here. Full speed ahead. Tell the bridge.'

Lund ran out of the room, and Johanson chased after her. Suddenly everyone on board was running. Johanson skidded on to the working deck, where sailors and technicians were shifting cold storage tanks under Lund's lead. The winch cable quivered as the Sonne accelerated.

Lund saw him and ran over.

'What was that?' he yelled.

'We hit a gas pocket. Look!'

She pulled him across to the railings. Hvistendahl, Stone and Bohrmann joined them. Two Statoil technicians had gone to the far end of the stern and were standing under the A-frame, peering down.

Bohrmann was gazing at the taut cable. 'What the hell is he playing at?' he hissed. 'Why hasn't the idiot stopped the winch?' He hurried back inside.

At that moment the sea started to bubble madly and white lumps shot to the surface. The Sonne had reached full speed. There was a clunking sound as the video-grab's cable tightened. Someone raced across the deck towards the A-frame, waving wildly. 'Get away from there!' he yelled to the pair from Statoil. 'Run!'

Johanson recognised him. It was the first officer, the Sheep-dog, as the seamen called him. Hvistendahl swivelled round, gesticulating. Then everything happened at once. A foaming, hissing geyser engulfed them. Johanson saw the outline of the video-grab rising through the surface of the water. An unbearable stench of sulphur filled their nostrils. The Sonne's stern sank, then the metal jaws shot sideways and sped through the air like a gigantic swing towards the topside. The second of the two technicians saw it coming and flung himself down. The other man froze, then took a tentative step backwards and stumbled.

The Sheep-dog sprang forward to pull him to the ground, but the metal jaws crashed into the man and sent him flying into the air. He fell back to the deck, skidded along the planks and lay still.

'Oh, God,' Lund gasped. 'Please, no.'

She and Johanson ran towards the motionless body. The first officer and other crew were kneeling beside him. The Sheep-dog glanced up. 'Don't touch him.'

'But I-' Lund began.

'Call the doctor.'

Johanson knew that Lund couldn't bear to be inactive. Sure enough, she walked towards the grab. It had nearly stopped swinging. Mud dripped from it on to the deck. 'Open it!' she shouted. 'Get whatever's left into the tanks.'

Johanson looked down at the sea. Bubbles of stinking methane were still fizzing up to the surface, but gradually subsiding. The Sonne was charging away from the scene. The last chunks of methane ice floated to the surface and disintegrated.

With a loud creak the grab opened its jaws, releasing hundreds of kilos of ice and sediment. Sailors and scientists crowded around it, trying to plunge the hydrate into tanks of liquid nitrogen. Johanson felt useless. He went over to Bohrmann to help collect the lumps. The deck was covered with small, bristly bodies. Some were twitching and writhing, but the majority hadn't survived the rapid ascent. The sudden change of temperature and pressure had killed them.

Johanson picked up a clump and examined it closely. Dark channels criss-crossed the ice, strewn with the corpses of worms. He turned it back and forth until its crackling and cracking reminded him that it needed to he conserved. Some of the other chunks were even more riddled with holes, but the real work of destruction had clearly taken place beneath the tunnelling. Crater-like breaches gaped in the ice, covered with slimy trails.

Johanson forgot about the storage tanks. He rubbed the slime between his fingers. It looked like the remains of bacterial colonies. Bacterial mats were found on the surface of hydrates: what were they doing inside the ice?

A few seconds later the lump had disappeared. He looked round. A muddy puddle covered the working deck. The man who had been hit by the grab was gone. Lund, Hvistendahl and Stone had also left the deck, but Bohrmann was leaning on the rails. Johnson joined him. 'What happened down there?'

Bohrmann ran his hand over his eyes. 'We had a blow-out. The grab penetrated more than twenty metres through the hydrates and gas came up. Did you see the enormous bubble on the screen?'

'Yes. How thick is the ice here?'

'Seventy to eighty metres minimum – at least it was.'

'So, the ice was cracked.'

'That's how it seems. We need to find out as soon as possible whether it's an isolated case.'

'You want to take more samples?'

'Of course,' said Bohrmann, testily. 'That accident should never have happened. The guy at the winch raised the grab when we were going full-speed. He should have stopped it.' He looked at Johanson. 'Did you notice anything unusual when the gas shot up?'