"No, keep our conversations private."

"Thought that's what you'd want."

The water reached his neck, then was soon over his head. It occurred to him then to wonder about what the submind had just said.

"How… will you know?"

"How will I know when you're speaking to me and not to your brother?" it said to him. "Remember, I'm your suit and I'm monitoring you on many different levels."

Cormac wasn't sure if he liked the idea.

A clear bell tone rang in the airlock and the water swirled around them as Dax pushed open the chainglass door.

"Let's go," he called, something odd in his voice.

Dax pushed off and drifted out into the sea, his suit immediately adjusting to give him negative buoyancy. Cormac peered down at the bottom twenty feet below, rocky and forested with weed, mussel beds lying between like spills of coal. As he pushed off he dislodged something from a ledge below the door and turned over on his back for a moment to observe a scallop jetting unevenly away from him. Now, in this position, he gazed back at what he could see of Tritonia. On either side the convex wall curved away, filled with viewing windows, many of them lit from inside and crowded about outside with undersea life attracted to the light. To his right he saw a robot crawling along the exterior of the structure, a clean trail behind it as it stripped away barnacles, a shoal of fish dogging its course as they tucked in to the bounty of shredded shellfish it provided. The machine looked like a large aluminium lizard with a wide flat head and a mouth like a manta ray's. It wasn't something that could be mistaken for a large iron scorpion. Cormac now focused on the undersea city's roof. Up there a secondary seabed had been provided and upon this had burgeoned a forest of kelp. He knew that now, up there about the numerous artificial islands and moorings, sea otters had become established, feasting on a cornucopia of abalone.

"Come on sea slug!" shouted Dax. "Shift yourself!"

Cormac rolled over again and kicked hard after his brother, who was lower down now, sculling over a bed of oysters and menacing a large edible crab with the barbed point of his harpoon. Once he saw Cormac coming after him, he kicked away above the crab, which held its claw high and scuttled backwards, falling over the edge of the oyster bed. Crab had been a menu favourite for over thirty years and despite the availability of the big GM sea farm versions, demand still outstripped supply. Cormac peered down at the crustacean as it righted itself and now raised its claws threateningly. It did look very much like one of the Prador, the difference being size, intelligence, and who was likely to eat who, though there had been news stories buzzing around the nets of some human soldiers trying a new addition to their diets. It was only fair, Cormac thought, the Prador showed no reluctance in adding humans to their menus.

The start of the reefs was marked by the Tesco III, which had been sunk by an eco-terrorist cruise missile over two hundred and fifty years ago. This had been during the time when Middle Eastern oil was both running out and being supplanted by fusion power. Cormac had studied some of the history of the time but found it boring in its repetition of idiocies stemming from the political corruption of science. The two-mile-long oil tanker was only vaguely recognisable as a ship under the masses of marine growth. Along one side was an entrance for divers who found such a claustrophobic environment enticing and who might enjoy hunting the massive conger eels that haunted the huge dark spaces inside. Dax increased his buoyancy and abruptly rose beside the wall of this tanker.

"Take me up," said Cormac, then abruptly felt himself rising too. As he went up he felt the breathing-assist of the suit beginning to slacken off as pressure decreased. He also felt other subtle adjustments as it sought to protect him from the pressure change.

He swam in closer to the cliff and studied the corals and multicoloured blooms of weed that owed their existence to a craze, over a century ago, for seawater fish tanks containing colourful GM seaweeds. Amidst these he observed numerous hermit crabs. Many of these had made their homes in a variety of natural whelk shells, but many others had found other quite odd-looking residences.

"What is all this stuff?" Cormac asked.

Dax replied, "Indestructiphones," but said nothing more.

"Mackerel?"

"Here you see the result of the industries, of the early twenty-second century, producing cheap and incredibly hard-wearing ceramics and glass," the submind replied. "Those are the ceramic cases of Indestructiphones, just like your brother said, also webcams, glass pipe fittings for plumbing and bottles and jars."

Cormac could see that some of the latter still bore inset labels of their erstwhile contents—coriander, mustard, tabasco, pickled ginger. He then paused to gaze at the ghoulish sight of a hermit crab that had taken up residence in the remains of a ceramic artificial hand.

Soon he passed the crumbling rails of the tanker and swam after his brother across the wide deck, now occupied by a garden of brain corals which, like all the corals in the vicinity, were no product of evolution, but had been adapted to grow fast and survive in the cold waters here. Beyond the ship the reefs proper began: corals stretching as far as they could see. Only by pausing and gazing for a long while could Cormac discern the regularity of this waterscape.

"Mackerel," he said, "what was it they dumped here?"

"One-hundred-year tyres," the submind replied. "They were carbon-filament tyres that gave even the most advanced recycling equipment of the time indigestion. They epoxied them together in tubes and dropped them to make a conservation area impossible to trawl."

"Was that before the Tesco got hit with a missile?"

"Yeah."

"So they were still trawling then?"

"Oh yeah—Oceana Foods was still struggling to get started and there were still pollution problems with the sea farms. You couldn't fart back then without some environmentalist following you about with a gas monitor."

"Should be there in a few minutes," called Dax, now a good hundred yards ahead.

Cormac swam harder to catch up, but Dax was not slowing down; in fact, as the sand-beds beyond the reefs came into view, he began swimming harder.

"There is something wrong with your brother," said Mackerel abruptly.

"Dax!" Cormac called. "Slow down!"

Soon Dax was low over the sand-beds swimming hard just above a shoal of fish. Something was stirring up the bottom and in a moment Cormac spotted the harpoon spear shoot down, its trailing string the bright orange of instantly clad monofilament. Dax was jerked down as something two yards wide and as long as Dax was tall took off along the bottom. Some kind of huge flatfish.

"What's he got?" Cormac asked, panting as he continued to swim hard.

"Turbot," Mackerel supplied. "They're big buggers out here—crossbred with escaped sea-farm stock from Oceana Foods."

"Right."

Dax was clinging onto his harpoon as the massive fish just kept on going. Now a trail of blood was streaming from the fish.

"Dax!" Cormac called again.

"No it's not," Dax replied. "They weren't… they weren't…"

"I have summoned help," said the submind.

Suddenly the great fish jerked and shuddered, coming up from the seabed. Cormac realised the harpoon gun must be the kind that could deliver a massive electric shock. The turbot was almost certainly dead now. It slowly turned over, exposing its milk-white underside, blood clouding around it.

"No… no it… no please. I didn't mean…" Dax's voice slowly lapsed into an indistinct muttering. He just hung in the sea, still clinging to his harpoon, still linked to the dead fish.

"You must return to your hotel now," said the submind.