No one spoke.

Vanderbilt's heavy jowls began to tremble and his entire body shook, as though a peal of laughter was mounting inside him. His fleshy lips twitched and he opened his mouth.

'I can see how that might be possible,' said Li.

The deputy director of the CIA looked as though he'd been stabbed in the ribs. His mouth closed. Then he wheezed, 'You can't be serious.'

'Oh, yes, I can,' Li said calmly. 'I didn't say Dr Johanson was right, but we should at least hear him out. He must have some evidence to support his claims.'

'Thank you, General. 'Johanson gave a little bow. 'I do.'

'Then please continue. Try to keep your explanation as succinct as possible so that we can start the debate right away.'

Johanson let his eyes rove round the room. Hardly anyone appeared openly dismissive. Most of the faces before him were frozen in surprise. Some looked fascinated, others disbelieving, and a few were impossible to read. Now he had to take the second step. He had to persuade them to assimilate his theory so that they could develop it on their own.

'Our main problem over the past few days and weeks,' he said, has lain in trying to connect the various phenomena. In fact, there wasn't any obvious connection until a jelly-like substance started to crop up. Sometimes it appeared in small quantities, sometimes in larger amounts, but always with the distinguishing characteristic that it disintegrated rapidly on contact with air. Unfortunately the discovery of the jelly only added to the mystery, given its presence in crustaceans, mussels and whales – three types of organism that could hardly be more different. Of course, it might have been some kind of fungus, a jellified version of rabies, an infectious disease like BSE or swine fever. But, if so, why would ships be disappearing or crabs transporting killer algae? There was no sign of the jelly on the worms that infested the slope. They were carrying a different kind of cargo – bacteria that break down hydrates and cause methane gas to rise. Hence the landslide and the tsunami. And what about the mutated species that have been emerging all over the world? Even fish have been behaving oddly. None of it adds up. In that respect, Jack Vanderbilt was right to discern an intelligent mind behind the chaos. But he overestimated our ability – no scientist knows anything like enough about marine ecology to be capable of manipulating it to that extent. People are fond of saying that we know more about space than we do about the oceans. It's perfectly true, but there's a simple reason why: we can't see or move as well in the water as we can in outer space. The Hubble telescope peers effortlessly into different galaxies, but the world's strongest floodlight only illuminates a dozen square metres of seabed. An astronaut in a spacesuit can move with almost total freedom, but even the most sophisticated dive suit won't stop you being crushed to death beyond a certain depth. AUVs and ROVs are only operational if the conditions are right. We don't have the physical constitution or the technology to deposit billions of worms on underwater hydrates, let alone the requisite knowledge to engineer them for a habitat that we barely understand. Besides, there are all the other phenomena: deep-sea cables being destroyed at the bottom of the ocean by forces other than the underwater slide; plagues of jellyfish and mussels rising from the abyssal plains. The simplest explanation would be to see these developments as part of a plan, but such a plan could only be the work of a species that knows the ocean as intimately as we do the land – a species that lives in the depths and plays the dominant role in that particular universe.'

'Have I understood you correctly?' Rubin asked excitedly. 'You're claiming that we share this planet with another intelligent race?'

'Yes.'

'If that's so,' said Peak, 'why haven't we heard of or seen them before?'

'Because they don't exist,' Vanderbilt muttered testily.

'Wrong,' said Johanson vigorously. 'I can think of at least three good reasons why we've never come across them. First, there's the phenomenon of the invisible fish.'

The what?

'Most deep-sea creatures can't see any better than we can, but they've refined their other senses. Their bodies respond to the slightest change in pressure. Sound waves are detected over hundreds, if not thousands of kilometres. No submersible could ever get in viewing range without attracting their attention. In theory, millions of fish could be living in a particular region but if they stuck to the shadows, we'd never find out. If that's true of ordinary fish, how are we supposed to spot intelligent beings? If they don't want us to see them, they – won't let us! Second, we have no idea what these creatures might look like. So far, we've filmed a few peculiar phenomena – a blue cloud, flashes that look a bit like lightning, and an odd thing on the Norwegian continental slope. Are those signs of alien intelligence? And what about the jelly? Or the noises that Murray Shankar can't identify? And, finally, the third reason. At one time we were convinced that life was only viable in the upper layers of the ocean, where sunlight penetrates. Now we know that the whole ocean is teeming with life, even at depths of eleven thousand metres. Many organisms don't need to seek out shallower water. In fact, most wouldn't survive the transition – the water temperature would be too high, the pressure too low, and they wouldn't find their usual food. We, on the other hand, are well acquainted with the surface of the water, but only a handful of robots and scientists in bulky submersibles have ever visited the depths. Imagine an alien spaceship lowering cameras to Earth. Each captures only a few square metres at a time. The first zooms in on the Kalahari Desert. The second takes a snap of the Mongolian steppes. A third is lowered over Antarctica, and the fourth hovers over a city and films just a few square metres of grass and a dog peeing up against a tree. What impression would the aliens have? No sign of intelligent life, though primitive life-forms are sporadically present.'

'They'd have to have some kind of technology to accomplish all this,' said Oliviera.

I've been thinking about that,' said Johanson. 'It strikes me that there's an alternative to technology as we know it. We use materials to create our equipment and tools – houses, vehicles, radios, clothes and so on. But sea water is far more aggressive than air. Only one thing matters in the depths: optimal adaptation. Living organisms are usually fantastically well adapted, so you could imagine a technology based entirely on biology. If we're assuming this race is highly intelligent, then it seems reasonable to suppose that it's also creative and has a detailed knowledge of the biology of marine organisms. I mean, we're doing it too, if you think about it. For thousands of years we've been using other life-forms as part of our inventions. Hannibal crossed the Alps with a herd of living trucks. Horses are a kind of sentient motorbike. We've been training animals throughout the course of history, but now we're able to genetically modify them as well. We're already cloning sheep. What if we take the idea a bit further? What if we imagine a race that has based its culture and technology entirely on biology? They'd simply breed whatever they need, whether for daily life, transport – or warfare.'

'God help us,' groaned Vanderbilt.

'Of course, humans use living organisms for warfare too,' continued Johanson, as if he hadn't heard. 'Scientists are growing strains of Ebola and other viruses, and experimenting with smallpox. For the moment, the conventional method is to cram them into warheads, but it's not the most straightforward way of doing things, and even satellite-guided missiles don't always hit their mark. Dispatching a pack of diseased dogs might be more effective. Or you could use a battalion of birds – or insects, for that matter. Just imagine trying to defend yourself against a swarm of virus-infested flies or an army of infected ants … Or against millions of crabs, transporting killer algae.' He paused. 'The worms on the continental slopes were genetically engineered. It's not surprising that we'd never seen them before. They didn't exist. Their sole purpose is to convey bacteria into the ice. They're annelid cruise missiles, if you like – biological weapons developed by a race of beings whose entire culture is based on manipulating organic life. It gives us an explanation for all the various mutations. In some cases, organisms have been modified only slightly, while others are new creations. Take the jelly-like tissue. It's a highly versatile biological product, but it certainly wasn't arrived at via standard evolution. Like the worms, it's there for a purpose – to control other living creatures by invading their neural networks. It's somehow affecting the behaviour of live whales. The crabs and lobsters are a slightly different story. The jelly steers their movements, but they're not actually alive. They're empty shells with incomplete nervous systems – organic spacesuits for the journey on to land.'