And now Pfiesteria piscicida was attacking Brittany lobsters.

But was it really Pfiesteria piscicida?

Roche was plagued by doubt. The organism was far more aggressive than he'd expected. The real puzzle, though, was how the lobsters had survived. Had the algae come from inside them? Was it mixed with the jelly-like substance? The jelly had decomposed on contact with air; he was sure it was a distinct phenomenon, something new. But had the algae and the jelly both been hidden in the lobster? And, if so, what had happened to its flesh?

Was it really a lobster at all?

Roche was stumped. But of one thing he was certain: the substance, whatever it might be, had entered Roanne's drinking water.

22 April

Continental Margin, Norwegian Sea

At sea the world was just water and sky, with little to tell them apart. There were no visual markers, which meant that on clear days, the sense of infinity could suck you into space, and when it was wet, you never knew if you were on the surface or somewhere beneath it. Even hardened sailors found the monotony of constant rain depressing. The horizon dimmed as dark waves merged with banks of thick grey cloud, robbing the universe of light, shape and hope in a vision of desolation.

At least in the North Sea and the Norwegian Sea, the numerous oil platforms provided landmarks, although from the edge of the continental shelf, where the Sonne had been sailing for the past two days, most were too distant to see. Now even the few rigs in view were shrouded in drizzle. The vessel and everyone on it was soaked. A clammy cold crept under their waterproof jackets and overalls. Plump raindrops would have been preferable to the never-ending trickle of water, which seemed to rise off the sea as well as fall from the sky. It was one of the most unpleasant days that Johanson could remember. He pulled his hood down over his head and made for the stern, where the technicians were raising a CTD probe. Bohrmann caught up with him half-way there.

'Seeing worms in your sleep yet?' asked Johanson.

'Not quite' said the marine geologist. 'What about you?'

'Oh, I'm pretending I'm in a film. It's kind of reassuring.'

'Good idea. Who's directing?'

'Hitchcock.'

'The deep-sea version of The Birds.' Bohrmann smiled wryly. 'Sounds intriguing… Ah, here we go!'

He hurried towards the stern. A circular cage of rods rose over the side of the boat, hanging from the arm of a crane. Its top half was covered with an array of PVC bottles, containing samples of water from varying depths. Johanson watched as the probe was hauled on board and the bottles removed. Then Stone, Hvistendahl and Lund appeared. Stone hurried over to him. 'What's Bohrmann saying?' he asked.

'Not much.'

Stone's belligerence had given way to dejection. The Sonne had been following the continental slope south-west to a point above the tip of Scotland, taking readings from the water, while a sledge-mounted video system filmed from below. It was a bulky piece of equipment, like a steel shelf packed with gadgets, that was towed along the seabed. It was equipped with sensors, a floodlight and an electronic eye that took pictures and sent them via optical cable to the control lab on board.

The Thorvaldson's footage came courtesy of the more up-to-date Victor. The Norwegian research vessel was following the slope in a north-easterly direction towards Tromso, taking readings from the Norwegian Sea. Both vessels had set out from the site where the unit was to be built and were now on course to meet. Two days remained until their rendezvous, by which time they would have navigated the slope from Norway to the North Sea and recharted it from scratch. It had been Bohrmann and Skaugen's decision to survey the area as though they were exploring new territory – which, as it turned out, was what the waters had become. Since Bohrmann had announced the first findings, nothing seemed certain any more.

The news had come in the previous morning, before the sledge's first pictures arrived on the screen. They'd lowered the CTD probe at first light, when the air was damp and cold. Johanson had tried to ignore the sinking sensation in his stomach as the boat pitched over the waves. The first samples were whisked away to the geophysical lab where they underwent analysis. Shortly afterwards, Bohrmann had summoned the team to the seminar room on the main deck. They sat at the polished wooden table, waiting expectantly and clasping mugs of coffee.

Bohrmann's eyes were fixed on a sheet of paper. 'The first results are available already,' he said. 'They're not representative, more a snapshot of what's going on.' His eyes lingered briefly on Johanson, then shifted to Hvistendahl. 'Is everyone acquainted with methane plumes?'

A young man from Hvistendahl's team shook his head.

'They form when free methane gas escapes from the seabed,' explained Bohrmann. 'The gas dissolves in the water, is pulled along by the current and rises to the surface. Usually plumes are found at plate boundaries, where one plate pushes beneath the other, causing sediment compaction and uplift. As a result, fluids and gases escape. It's a well-known phenomenon.' He cleared his throat. 'Areas of high pressure like this are common in the Pacific but not in the Atlantic – and certainly not around Norway. The boundaries here are mainly passive. But this morning we picked up a highly concentrated methane plume. It doesn't figure in any of the earlier data.'

'What level of concentration?' asked Stone.

'Worryingly high – on a par with the levels we found off the coast of Oregon. And that was in a fault zone.'

'Right.' Stone smoothed the frown from his forehead. 'Well, to my knowledge, methane is always leaking into the water around here. I've seen it countless times. It's a well-known fact that somewhere on the seabed gas is constantly escaping. There's always a reason for it. I don't see any call for panic.'

'I don't think you quite understand.'

'Now, look here,' said Stone, 'all I care about is whether or not there's cause for concern. If you ask me, there isn't. We're wasting our time.'

Bohrmann smiled amicably. 'The slope in this region, Dr Stone, especially to the north of here, is held together by methane hydrates. The layers of hydrate are sixty to a hundred metres deep – that's a hefty wedge of ice keeping the seabed in place. However, we're aware of vertical breaks in the layers. Gas has been escaping through them for years. Theoretically, it shouldn't happen. At such high pressure and low temperature, it should freeze on the seabed. But it doesn't. That's the gas you were referring to. We can live with it – we can even decide to ignore it. But we shouldn't let our graphs and tables make us feel complacent. I'm telling you, the concentration of free gas in the water is excessively high.'

'But is it really a seep?' asked Lund. 'Is the gas in the water escaping from the crust, or is it coming from-'

'Dissociated hydrates?' Bohrmann hesitated. 'That's the big question. If hydrates are dissociating, it means the parameters have changed.'

'And is that the case here?' said Lund.

'There are only two parameters affecting the stability of the hydrates: pressure and temperature. But we haven't detected any rise in water temperature, and the sea level hasn't altered.'

'What did I tell you?' said Stone. 'You're worrying about a problem that doesn't exist. So far, we've only seen one sample.' He looked to the others for support. 'A single bloody sample.'

Bohrmann nodded. 'You're right, Dr Stone. We're speculating. But we'll find out the truth. That's why we're here.'

JOHANSON AND LUND HAD headed for the canteen. 'Stone's getting on my nerves,' Johanson said. 'He's always trying to undermine the tests. What's wrong with him? It's his bloody project.'