Bauer missed comfy armchairs, trees, birds and German beer. Now he missed Weaver. He'd grown fond of the determined young woman, and he'd begun to see the point of what she did. Getting the public interested in your work meant using a vocabulary that wasn't a hundred per cent accurate, but that everyone could follow. Weaver had made him realise that all his work on the Gulf Stream would be lost on people if he couldn't explain how the current started or where it flowed. At first he hadn't believed her. Just as he'd refused to believe that no one had heard of drifting profilers, until Weaver had convinced him that they were too new and specialised. But not knowing about the Gulf Stream? Weren't children taught anything at school?

Weaver was right that his work needed public exposure: he could broadcast his anxiety and put pressure on the culprits. And Bauer was worried.

The source of his troubles lay in the Gulf of Mexico, where temperate surface water flowed from Africa along the coast of South America. Warmed by the sun in the Caribbean basin, it continued northwards, an inviting stream of salty water that remained on the surface because of its heat. The Gulf Stream, Europe's mobile heater, wound its way north, carrying a billion megawatts of warmth, equivalent in energy to 250,000 nuclear power stations. It travelled as far as Newfoundland where it mingled with the cold waters of the Labrador Current and dispersed. Some pinched off to form eddies, swirling rings of warm water that meandered northwards as the North Atlantic Drift. Prevailing westerlies saw to it that plenty evaporated, conferring ample rain on Europe and causing the water's salinity to soar. Dubbed the Norwegian Current, the water continued along the coast of Norway through the North Atlantic, staying warm enough to allow ships to dock in south-west Spitsbergen even in mid-winter. It was only when it reached Greenland and northernmost Norway that the stream of heat was halted. There, it hit the Arctic, where the icy ocean and chill winds cooled it rapidly. The Gulf Stream had always been very salty; now it was immensely cold too. The heavy water fell, sinking vertically – not as a front but in channels of water called chimneys, which were difficult to pinpoint since they moved with the swell. Convective chimneys measured twenty to fifty metres across, with ten or so clustered in the space of a square kilometre; but their exact position varied daily, depending on the wind and waves. The critical point about them was the suction effect the sinking water caused. This was the Gulf Stream's real secret: it didn't flow north but was drawn there, sucked onwards by the powerful pump at the bottom of the Arctic. When the icy water reached a depth of between 2000 and 3000 metres, it started on the return leg. It was a journey that would take it once round the world.

Bauer had released a batch of floats in the hope they would follow the path of the current, but trying to find the chimneys in the first place was difficult enough. They should have been everywhere. Instead the giant pump seemed to have packed up entirely or begun its work elsewhere.

Bauer had come here because he was aware of the problem and he knew what would follow. He hadn't expected to find things working perfectly, but he wasn't prepared to find nothing at all.

It was seriously worrying.

He'd confided his concerns to Weaver, before she'd left him. Since then he'd been updating her and entrusting her with his innermost fears. Several days ago his team had detected a dramatic rise in the methane content of the water. Now he was considering the possibility that it was linked to the disappearance of the chimneys. He was almost sure of the connection. Hunched over his data, Bauer examined stacks of calculations, diagrams and charts. Every now and then he emailed Karen Weaver to tell her of his latest findings.

He was so caught up in his work that he was oblivious to the shaking. His teacup made its way to the edge of the table and toppled over, pouring its contents on to his lap. 'Oh, blast,' he muttered. Hot tea soaked through his trousers and down his legs. He got up to examine the extent of the damage.

Suddenly he stiffened, straining to hear the noises outside.

Screams. Someone was screaming. Heavy boots pounded the deck and the ship vibrated furiously, throwing him off balance. Groaning, he collided with his desk. The ground fell away beneath him, as though the vessel had fallen into a hole. Bauer sprawled backwards and fear took hold of him. He scrambled to his feet and stumbled into the passageway. The shouts were louder now, and the engine started up. A man was yelling in Icelandic. Bauer couldn't understand the words, but he could hear the terror, which was echoed and amplified in the voice that replied.

Had there been an underwater earthquake?

He hurried along the passageway and down the stairs to the deck. Fierce vibrations rocked the ship, making it hard to stay upright. He pushed his way unsteadily to the hatch, and was hit by the stench. All of a sudden Lukas Bauer knew what was wrong.

Struggling to the rail, he looked out. The water was seething with bubbles.

There was no swell. No sign of a storm. Just thousands of giant bubbles, surging to the surface.

The boat plummeted again and Bauer toppled over, crashing face first on to the deck. Pain exploded in his skull. When he raised his head, his glasses were broken. Without them he was blind, but he didn't need lenses to know what happened next. The sea rose up and closed over the vessel.

Oh, God, he thought. Oh, dear God, no.

30 April

Vancouver Island, Canada

The night was resplendent in deep shades of green. It was a while since Anawak had first started to fall through the shadowy universe, but now a rush of euphoria swept through him, and he stretched out his arms, plummeting downwards like an Icarus of the depths, weightless and elated. He sank deeper and deeper. Something shimmered in the distance below him, a frozen white landscape, and all at once the sombre ocean became a dark night sky.

He was standing at the edge of an icefield, gazing at the deep, still water, with a wealth of stars above him.

He was at peace.

How wonderful it felt to be standing there. In time, an ice floe would form, detaching itself from the frozen water and drifting through the seas, carrying him north to a place where he would be free from the burden of questions. Anawak's chest swelled with longing and tears came into his eyes, dazzling him. He shook his head, dispersing the drops, which scattered over the sea, lighting up its darkness. Something rose towards him from the depths, and the towering water became a figure. It waited for him at a distance, too far for him to follow. Shiny and motionless it stood there, starlight trapped within its surface.

I found them, it said.

The figure had no face and no mouth, but the voice was familiar. He took a step towards it, but he was at the water's edge. A vast and terrifying presence lurked beneath him in the darkness.

What did you find? he asked.

The sound of his voice made him start. The words dropped heavily from his mouth. What the figure had said or maybe thought had sounded noiseless; now his voice shattered the silence that had filled the landscape of ice. Biting cold took hold of him. He looked for the thing in the water, but it was gone.

Surely you don't need to ask? a voice said beside him.

He turned his head and saw the delicate figure of Samantha Crowe, the SETI researcher.

You sound awful, she said. You're fine at everything else, but you need to practise talking.

Sorry, he stammered.

I've found my aliens. Do you remember? We finally made contact. Isn't that great?