Visibility is zero. Only the top layer of oil, exposed to air, can burn; the rest of it, opaque as ink, blocks the sun's light entirely. Only the telltale pinching sensation inside her ears tells her she is sinking. Danielle works her jaw furiously, opening the eustachian tubes to equalize air pressure before her eardrums burst or her sinus cavities rupture. With her free hand she pushes the inflation button on her buoyancy vest, her BCD, flooding its bladders with enough air to slow her descent. All this in only a few seconds, operating purely on instinct. She hasn't gone diving for years, but the shock of immersion has brought it all back, made that summer in Baja California seem like yesterday.

She feels a disturbance in the water to her left. A splash. Keiran made it off the ship. But he is helpless, doesn't know the first thing about diving, she can't even see him, and her fins aren't on, she can't maneuver. Danielle reaches her arm out, clutching desperately, and her fingers close on something. A strap. Enough to connect them in the dark water. He is not as overweighted as she, he is sinking, but much slower than she had. She grabs him and pulls him closer. She can tell by feel that he is curled up into a taut ball around the scuba tank he carries, breathing as furiously as an Olympic sprinter. But at least he isn't kicking and flailing.

Even so, their situation is desperate. Both of them are sinking, she thinks fairly slowly, and that is a good thing, but she can't even see her gauges to see how deep they are. They don't dare ascend for fear of surfacing in the midst of the flames; and if they go too deep, nitrogen narcosis will set in like a powerful drug, they will lose their ability to reason, and even if they somehow manage to ascend after that, they will certainly get the dreaded bends. They need to get out from under the burning oil right now. But without fins, in full scuba gear, Danielle can't swim much faster than an infant crawls. And they may well sink to a lethal depth before she can even strap on her fins.

She takes a deep breath and tries to focus. No sense brooding about their predicament; better start trying to do something about it. She lets go of the speargun, she can't spare a hand for it, tucks an arm through one of Keiran's straps to keep them connected, and then, working awkwardly in darkness so complete she might as well be blind, with thick gloves on, she slips off one of the fins looped around her arm, and tries to pull it onto her right boot as fast as she can. The attempt is not successful. But after its failure she realizes she can see a metallic glint in front of her. She squints and it coagulates into the rim of the spare tank Keiran carries. Vision has returned.

Of course: as they sink, they fall out of the cone of darkness beneath the oil, to where ambient sunlight can reach them at an angle from the edge of the slick. She quickly looks at her gauges. They are a hundred feet deep already. Danielle relaxes when she sees this. It's farther down than she'd like, but they can manage a good ten minutes at this depth before it gets dangerous, time enough to get themselves together.

Something drifts through the corner of her sight. The edges of her mask are clouded, they weren't able to spit and clean them out with seawater, she can only see clearly straight ahead. She turns her head, sees the discarded speargun drifting slowly downwards, and reaches out to grab it. Maybe they can afford to keep it after all.

Keiran, thankfully, is following instructions, remains a motionless lump wrapped around the spare scuba tank. His whole body is shuddering. The water around them is extremely cold, and it takes a minute or two for body heat to warm the water between wet suit and skin, but Danielle knows Keiran's spasms are not due to the temperature. He is fighting panic, and the need to do something instead of trusting his life to Danielle, with every iota of his will. So far he is winning. She finds his BCD's controls, inflates him to neutral buoyancy so he will hover near a hundred feet deep, and then, with slow precise movements, keeping an eye on him, straps the fins onto her feet.

The difference is enormous; she is able to maneuver and swim again, in a way impossible without fins. She carefully puts the last two fins on Keiran's feet as well, then takes him by the arm and begins to swim towards the light. After a moment he catches on and starts to kick furiously as well. Moving awkwardly, encumbered by the spare tank and speargun, it takes them several minutes to swim a few hundred metres, past the furthest edge of the oil slick. Danielle makes sure they ascend as they go, to save air, improve visibility, and minimize their risks of nitrogen narcosis and decompression sickness.

About halfway there, the water around them suddenly roils violently. Then a powerful current sucks them backwards and down. Even though they are kicking as hard as they can, they drop thirty feet in a few seconds, making Danielle's ears pop painfully, before the disturbance ends as suddenly and mysteriously as it began. She keeps moving, utterly bemused. Nothing like that has ever happened to her while diving. She's never even heard of anything like that. Then she realizes: the eddy current from the ship, as it sank. As if the sunken vessel was trying to reach out with its last pulse of strength, drag them down to join it in Davy Jones' much-fabled locker. Had they been a little further back they might well have been sucked down. She hopes that's what happened to Laurent.

Danielle keeps kicking. Her legs are tired, but at least the exertion helps fight the cold. By the time clear unslicked ocean is above them, they are only twenty feet deep. Danielle inflates Keiran's BCD and hers a little further, and slowly, finger on her BCD purge valve, ready to descend again if the air is too hot or smoky to breathe, they ascend to the surface. Keiran's breath has slowed a little, but he has already used half of his air. Danielle has consumed less than a fifth of hers.

The transition from water to air is as always disorienting. It feels a little like being born. They are downwind from the thick black cloud that obscures the ship, a cloud fed by ten thousand tongues of flame beneath it, but smoke rises; the air here at sea level is clear. And the warmth from the flames is welcome after immersion in near-freezing water. Danielle lifts her regulator from her mouth and takes a tentative trial breath. The air is clean and cool. She inflates Keiran's BCD, and then her own, so they act as life preservers, holding their heads above the waves, and gently pulls the regulator from Keiran's mouth. He bit down on its rubber mouthpiece so hard that his mouth is bleeding, but his eyes are focused, he seems otherwise okay.

"You all right?" she asks.

He says in a shaking voice, "I don't think I like scuba diving."

"It's more fun under better circumstances."

"I'll take your word for it. Do we have to go back down?"

"Probably not," she says.

He releases a deep sigh of relief. "Thank Christ for that. Now what? Wait for help?"

"Yeah. I hoped one of the lifeboats would come free and float loose when the ship sank. But I guess not."

"You never know. We'll see when the smoke clears. Looks like it's letting up."

The smoke does seem to be thinning out, and the edge of the flaming oil slick already seems further away than it did when they reached the surface. The oil is finally burning itself out. She hopes Keiran is right and a lifeboat somehow survived the sinking and the inferno. It is at least possible, they are made of metal, and would have been shielded from the flames right up until the ship sank. With no lifeboat, they will have to hope that help arrives very soon. It isn't water or sharks that will kill them. It is the cold. Even these full wet suits will only protect them so long in the North Pacific water. It is only hours, not days, until they freeze to death.

"Holy Christ," Keiran says.

Danielle follows his gaze and gasps. A lifeboat has survived. And it is occupied. She stares at the twenty-foot-long metal hull as it emerges from the cloud of black smoke, carrying two men in fire-ravaged scuba gear. Their suits have melted and run ragged on their bodies, burning the skin right off their body in places, leaving raw patches of muscle soaked with blood. The lifeboat's metal hull is marbled and warped with the heat. The men's faces are awful to look at; their lips have been burned away, and sheets of charred skin hang loose from their cheeks, reminding Danielle horribly of roast chicken. They are still alive, still moving, but not for long.

"Oh my God," Danielle says, her voice low. They must have gambled that the ship would not sink before the fires burned out, and lost. Maybe they were inexperienced divers, and didn't dare make the jump into the sea. Maybe they didn't put on weights, bobbed up to the surface, and desperately pulled themselves into the lifeboat as they burned.

But Laurent is not an inexperienced diver. He has told her tales of diving off Djibouti when he was with the Foreign Legion. And the fact that the dying men on the lifeboat had time to put on scuba gear means that he did too. And that, in turn, means that Laurent too is alive somewhere in this ocean around them, and very likely not alone. Danielle holds her speargun tightly. It seems like an inadequate weapon, now. Do they get on the lifeboat, and call attention to themselves? Or do they wait, hope to remain hidden in the waves of the North Pacific, and hope that help somehow finds them?

The decision is taken away from her when one of the near-corpses raises a shaking arm and points somewhere in the distance, about a hundred feet away from Danielle. Somehow the charred victims on the boat muster enough strength to ship oars in its oarlocks and begin to paddle the lifeboat towards whatever they have seen. Danielle cannot see over the waves, but that has to be Laurent and any surviving companions.

The lifeboat is moving too fast to catch. She watches as two men and a woman in untouched wet suits climb the ladder on its back. One of them pulls off his scuba hood. Laurent. The other man is Vijay. The woman is Sophia. She seems weak, and Laurent has to pull her onto the lifeboat.

The first thing Laurent does, when on board the lifeboat, is to disconnect the scuba tanks from the two burnt human wrecks, the two men who just spent their dying strength to get to him. And then, in an act so astonishingly callous it makes Danielle gasp, he pushes them out of the lifeboat, into the ocean. They are too weak to resist.

"What did he do that for?" Danielle asks, her voice low. "There's help coming."

"They don't know that," Keiran says. "After I sent the SOS I shut down the ship's communications. As far as they know they have to paddle to America."

"Good. Then they'll leave us here. They'll figure we'll just die in the water. They won't waste time looking for us."

And indeed Laurent and Vijay waste no time turning the lifeboat to the east and beginning to paddle. Sophia doesn't help; she collapsed weakly into the lifeboat, coughing violently.

"This is good?" Keiran asks.

"I don't know. But we've got a chance. If someone gets here in time."

Danielle looks at the lifeboat, still only a hundred feet away. She is armed, and they are not. If she could somehow sneak up on it – but she can't swim as fast as they paddle.

"Do you think they'll make it?" Keiran asks.

"If anyone will it's probably Laurent," Danielle says grimly.

"Shit."

"Yeah. Wait." An idea races into her mind, like an electric shock.

"What?"

"We can't let him get away. This will all start over again. Even if it doesn't we'll be looking over our shoulders for the rest of our lives."

"Too late," Keiran says. "He's gone."

"No he isn't. Give me that tank."

He looks at her for a moment, and then his eyes widen with comprehension. "You can not be serious."

"Give me that tank," Danielle repeats, not letting herself think about what she intends to do with it. "This is the only chance we'll ever get."

Keiran shakes his head violently. "No. No, let me do it. I'll do it."

"Don't be an idiot. Who's the divemaster here? Stop wasting time. Give me the tank."

Keiran passes the spare tank over wordlessly.

"Wish me luck," she says.

"Don't do this. This is insane."

"Close enough." She purges her BCD and descends back into the ocean.

Danielle levels off at about fifteen feet, close enough to the surface for good visibility, deep enough that she will not leave a visible trail. She rotates so she is facing directly away from the lifeboat, holds the extra scuba tank tightly to her chest, and twists open its nozzle.

Air pressurized to 5000 pounds per square inch, or roughly 400 atmospheres, roars out of the tank she holds. And, as Isaac Newton once observed, for every action there is an equal and opposite reaction. The tank, and the woman holding onto it, are propelled in the exact opposite direction, and at considerable speed.

It is like holding onto a small rocket; the tank shakes in her hands so violently that her teeth rattle, it is impossible to hold a steady course, and she has to look over her shoulder to see where she is going. But as she zigs and curls her way through the Pacific, holding her improvised compressed-air engine with an iron grip, speargun under her arm, she sees a shadow appear on the otherwise unbroken surface of the water behind her. She approaches it until the convex shape of the lifeboat's hull is visible, protruding into the water. Her jury-rigged underwater rocket grows weaker and weaker as she approaches, but by the time it finally runs out of air, she is a good thirty feet ahead of the lifeboat.

Laurent and Vijay are inside the boat, and her scuba gear is too heavy to be able to just lift herself out of the water, especially while holding the speargun. She must rely on that which killed the cat. Danielle moves up to about ten feet deep, and as the prow of the lifeboat approaches her position, she lets go of the empty scuba tank. It floats up and hits the hull with a metal-on-metal thunk that Danielle hears even underwater.

Danielle watches, speargun in one hand, the other on her BCD controls. She has to remind herself not to hold her breath. A moment passes. And she sees a dark face, shimmering through the water, appear over the lifeboat's gunwal. Vijay. He doesn't see her; it is far easier to see out of water than in.

Danielle doesn't hesitate. Her finger depresses the buoyancy valve, flooding her BCD with air. She flies upward, pops out of the ocean like a cork, and pulls the trigger. From four feet away it is impossible to miss. In Baja she saw spears go right through groupers almost a foot thick. This spear hits Vijay in his throat. He topples backwards into the life-boat. Danielle quickly descends back to fifteen feet deep. There is another bolt strapped to the side of the speargun. She has never armed a speargun before, but she's seen it done, and like most things that have to be done underwater it has been made idiot-simple, nothing but inserting it into a hole and turning a reel like a fishing pole's until it clicks.

She has probably just killed a man. Her only regret is that it was Vijay and not Laurent, far more dangerous. Now that the die is cast she thinks of Laurent with murderous rage. This has to end, he has to end, for all the awful things he has done, and all he will do if he gets the chance.

It won't end here if he doesn't want it to. All he has to do to get away is just keep paddling. He is safe inside the lifeboat, she won't be able to catch him. But Danielle is certain, dead certain, that he will not let her go like this. He will come after her.

A splash on the other side of the boat confirms it. Danielle aims the speargun at the new body in the water, is about to pull the trigger – and just as she realizes this figure is too small to be Laurent, there is another splash, directly above her.

She looks up and sees a large form plunging towards her, another diver. Laurent. He must have seen her air bubbles on the surface. He threw Sophia in first, as a distraction. She thinks all this in a flash as she raises the speargun and pulls the trigger, which she only barely has time to do, because then he is on her, an arm wrapping around her throat, he has knocked the speargun away, she is struggling but he is behind her and they are falling dangerously fast, she can't breathe, she manages to wriggle an arm into space between her neck and his meaty forearm but she still can't breathe, she tries to suck air from her tank but there is nothing there. He has turned off her air. And they are plunging deep into darkness.