Worms can't destabilise the hydrates, Bohrmann heard himself saying.

True. But that wasn't their purpose. They were only there to transport their consignment of archaea through the ice, like shuttle buses: next stop, methane hydrates, depth of five metres, alight here, time for work.

Why didn't we think of it before? thought Bohrmann. Fluctuating water temperatures, a decrease in hydrostatic pressure, earthquakes – all that was part of the hydrate expert's standard litany of doom. Whereas bacteria – everyone knew what they did down there, but no one had stopped to think about it. Not even in their worst nightmares had anyone envisaged an invasion like this. A methanotrophic suicidal worm? The sheer numbers of them; their distribution across the full length of the slope. It was absurd, inexplicable – even without the armies of archaea, driven by their deadly appetite, too many of them to imagine.

And he couldn't help thinking, how the hell did they get there? What are they doing there? What could have brought them?

Or who?

'The problem,' Mirbach was saying, 'is that our first simulation was based on largely linear assumptions. But real life isn't linear. We're dealing with developments that are chaotic and, in some cases, exponential. The ice is crumbling, which means gas shoots up from inside it, cracking more of the hydrates, so the seabed starts collapsing and the crisis point comes much-'

'OK, OK.' Bohrmann waved his hand. 'How long have we got?'

'A few weeks. Or days. Or even…' Mirbach hesitated. 'But we still can't be certain – I mean, we can't say for definite that it's really going to happen. All the evidence suggests it will, but it's such an unusual scenario. We can't prove a thing.'

'Cut to the chase, Yvonne. What do you think will happen?'

'I don't know.' She paused again. 'OK, say three army ants crossed the path of a mammal. They'd be stepped on and squashed. But if the same mammal were surrounded by thousands of army ants, they could eat it alive. That's how I imagine it is with the microbes. Do you see?'

'Call Johanson,' Suess repeated. 'Tell him we're predicting a Storegga Slide.'

Bohrmann exhaled slowly. He gave a silent nod.

THORVALDSON, Norway

They were standing on the edge of the helipad, looking down on the fjord. On the other side of the water, the shore was barely visible. The lake stretched out like tarnished steel beneath the greying sky.

'You're such a snob,' said Lund, jabbing a finger at the helicopter.

'Of course I am,' replied Johanson. 'But since I was press-ganged into this business, I think I've got the right to be picky.'

'Oh, don't start that again.'

Anyway, you're just as bad, insisting on driving around in my jeep.'

Lund smiled. 'Well, give me the key.'

Johanson fumbled in his coat pockets and pulled it out. He placed it in her palm. "

Take care of it while I'm gone.'

'You can count on me.'

'And no funny business with Kare.'

'In the jeep? I'm not that kind of girl.'

'I know what you're like. Anyway, at least you took my advice about defending poor Stone. He can fish his own bloody prototype out of the water.'

'I hate to disappoint you, but your advice didn't count. His reprieve was Skaugen's doing.'

'So he has been reprieved?'

'There's a chance he'll keep his job, if he can get things back on track.' She glanced at her watch. 'He'll be heading off in the submersible any time now. Wish him luck.'

'Why isn't he sending down a robot?'

'Because he's nuts. Actually, I think he wants to prove that in a crisis you need to do things his way. No one can handle it better than Clifford Stone.'

'And you're all letting him do it?'

'He's still the boss. Besides, in some was he's right. He'll get a better picture that way.'

Johanson had a vision of the Thorvaldson in a seascape of blurry greys, with Stone deep in the water beneath the keel, enshrouded in darkness and sinking towards the unknown. 'Well, you can't fault his courage.' He picked up his bag and they made their way to the helicopter. Skaugen had kept his promise and had loaned him Statoil's flagship model. It was a Bell 430, the last word in helicopter comfort, with minimal noise.

'About this Karen Weaver,' said Lund, as they stood outside the cabin door. 'What's she like?'

Johanson's eyes twinkled. 'Young, unbelievably pretty… How should I know?'

Lund flung her arms round him. 'You will take care of yourself, won't you?'

Johanson patted her back. I'll be fine. Why shouldn't I be?'

'No reason.' She was silent for a moment. 'Your advice wasn't entirely wasted, by the way. Those things you said to me – they made up my mind.'

'To see Kare?'

'To see things differently. And to see Kare.'

Johanson smiled. Then he kissed her on both cheeks. I'll call as soon as I get there.'

He climbed inside and threw his bag on to one of the seats behind the pilot. There was room for ten passengers but he had the cabin to himself.

'Sigur!'

He turned back.

You're the best friend I've got.' She lifted her arms helplessly, then dropped them. 'What I'm trying to say is-'

'I know.' Johanson grinned. 'You're no good at this kind of thing. Me neither. The more I like someone, the more of a mess I make of telling them. But I've never made more of a mess than the one I made with you.'

'Was that a compliment?'

'The best.' He closed the door. The pilot set the blades in motion, and the Bell lifted into the air, dipped its nose and flew out towards the fjord, leaving the research centre behind. Johanson made himself comfortable in the cabin, and tried to look out of the window, but there wasn't much to see. Trondheim was veiled in mist, and the lakes and mountains passed in a monotony of grey. The uneasy feeling was back.

It's only a ride in a helicopter, he told himself. No need to worry. He had methane and monsters on the brain, that was all. And the weather didn't help. Maybe he should have had a decent breakfast. He pulled Walt Whitman out of his bag and started to read.

The rotors throbbed dully above him. His coat, with his mobile in the pocket, lay crumpled on the seat behind him. He didn't hear it ring.

THORVALDSON, Norwegian Continental Slope

Stone had decided to say a few words before he climbed aboard. The cameraman would film him while the other guy took stills. He meant the entire operation to be documented properly. Clifford Stone was a professional; a man who never shirked his duties. This would serve as a reminder.

'A little further to the right,' said the cameraman.

Stone moved, ushering a pair of technicians out of the frame. Then he thought better of it and beckoned them back. 'Stand behind me,' he said. 'A little to the side.' He didn't want people thinking there was anything amateur or gung-ho about this mission.

The cameraman cranked up the tripod.

'Are we ready yet?' yelled Stone.

'Just a moment. It's still not right. You're in the way of the pilot.'

Stone took another step to the side. 'How's that?'

'Better.'

'OK,' said the cameraman. 'We're rolling.'

Stone looked into the camera. 'In a few minutes we'll be beginning our descent, with the aim of establishing what's happened to the prototype. At present it looks as though the unit has, er, moved from its original, er, its original… well, from the place where it… Oh, bother.'

'Not to worry. Start again.'

This time everything worked fine. Stone explained in a business-like manner that over the next few hours they would be searching for the prototype. He gave a short summary of the information they had so far, mentioned the changed morphology of the slope, and said that the unit must have subsided due to local destabilisation of the seabed. It all sounded very earnest. Perhaps a little too earnest. Normally famous explorers had something clever to say at the start or the end of their mission, Stone thought. Something that summed it up perfectly. One small step for a man, one giant leap for mankind. Now, that had been inspired. Of course, Neil Armstrong would never have come up with a line like that himself. They must have made him practise it beforehand, but all the same…Julius Caesar: I came, I saw, I conquered. Had Columbus made a famous quip? Or Jacques Piccard?