Read Chapter 1: High Tide Warning

The horn came first, as it always did. A long, mournful blast that rolled across the water like a dying thing. Finn heard it echo off the leaning towers of the low zone, and he checked his watch by the glow of the boat's corroded console. Twenty-three minutes to full tide. He had maybe fifteen before the curfew skiffs started running the channels in earnest.

He gunned the motor, a coughing two-stroke that had seen better decades, and the flat-bottomed skiff lurched between the drowned shopfronts of what had once been a high street. Billboards two storeys up still advertised perfume and holidays. Now they were nesting platforms for gulls and the occasional sniper.

The cargo sat under a tarpaulin in the stern: three sealed crates of lithium cells, stolen from a decommissioned substation up in the green zone, destined for a clinic in the marsh settlements that had no official power allocation. Finn didn't ask questions. He moved things. That was his job. That was his life.

The channel narrowed as he steered through a gap where a cinema had collapsed into the street, its marquee still legible beneath the green scum of the waterline. He killed the engine and let the skiff drift, using a long pole to push off the submerged wreckage. Here, sound carried. He could hear the hum of the barrier wall ahead, a deep and constant thrum that never stopped, day or night. The city's heartbeat, the engineers called it. The low zone's death sentence, everyone else called it.

Then he heard something else. A machine whine, sharp and electric. Not a skiff. Something with more power. Something that didn't belong in this part of the flood.

Finn poled the boat into the shadow of a derelict bank, its marble columns streaked with salt and algae, and waited. The whine grew louder, and through the gap in the buildings he saw it: a maintenance submersible, sleek and black, moving against the current with the ease of something that owned the water. High-zone markings on its hull, a red and gold band that might as well have been a crown.

It wasn't supposed to be here. Maintenance subs ran the deep channels near the wall, where the pressure valves and the turbine intakes needed constant attention. They didn't come into the low zone. Nothing official came into the low zone, except the enforcers and their taxes.

Finn's hand drifted to the old flare gun under his seat. He watched.

The sub slowed near the base of the barrier wall, where the ancient masonry met the newer flood defense concrete. A hatch on its underside opened with a hydraulic hiss he could barely hear over the wall's hum, and something dropped into the water. Small. Compact. It sank for a moment, then deployed a small flotation bladder and bobbed to the surface, blinking a faint red light in the darkness.

An encrypted beacon. Finn had seen them before, used by the wall crews to mark maintenance points or relay diagnostic data. But those were always bright yellow and stamped with safety warnings. This one was black, barely bigger than his fist, and it had no markings at all.

The sub's whine shifted as it turned, and Finn pressed himself deeper into the shadow. Its lights swept across the water, briefly catching the crumbling facade of the bank, then moved on. The sub slid away, heading back toward the deep channel, and was gone within a minute.

Finn waited another full minute. Still. The tide was rising, a slow push of brown water that carried the smell of sewage and diesel and something older, rustier. He poled the skiff out of the shadow and glided toward the beacon. It blinked at him as he approached, a patient red pulse in the gloom.

He knew he should leave it. Whatever the high zone was doing here, it wasn't his business. His business was lithium cells and clinic generators and not getting caught. Interfering with high-zone equipment was a fast way to disappear. The enforcers didn't take prisoners in the low zone. They took trophies.

But the beacon was small, and it was black, and it was sitting against the wall that held back the water that would one day swallow everything. Finn hooked it out of the water with his gaff and wrapped it in oilcloth before it could blink at anyone else.

The horn sounded again. Full tide in nine minutes. He shoved the pole against the bank and pushed hard, the skiff sliding through the narrow gap and out into a wider channel that ran parallel to the wall. He could see the floodlights of the barrier station ahead, where the enforcers kept their skiffs moored. He veered left, toward the old tube entrance.

He almost made it.

The spotlight hit him from the side, a white blade that sliced through the gloom and pinned him against the water. Finn didn't look at it. He dropped the pole, grabbed the tiller, and opened the throttle. The two-stroke screamed, and the skiff shot forward, spraying a wake that slapped against the walls of the drowned buildings.

The horn of the enforcer skiff was shorter, angrier. It barked twice. Then a siren. Then a voice over a loudhailer, distorted and clipped with that high-zone accent that treated every word like an accusation.

"Halt. You are in a restricted zone. Halt immediately or we will disable your vessel."

Finn didn't halt. He knew the channels. He'd been running them since he was twelve, when his father first put him on a boat and told him the water didn't forgive stupidity. The enforcers had fast skiffs and better engines, but they didn't know the shortcuts. They didn't know where the streets used to be.

He cut hard right, between two half-submerged office blocks, and the skiff bounced off something beneath the surface with a shuddering thud that rattled his teeth. The tarpaulin shifted, and he heard a crate slide. He didn't stop. The channel curved, and he leaned into it, the boat leaning with him, water spilling over the gunwale and soaking his boots.

The spotlight found him again. A gunshot cracked, and water spat up a few meters to his left. Warning shot. They never aimed to miss twice.

He reached the old tube station entrance, where the steps went down into the black water and the escalators had long since rusted into jagged metal teeth. The enforcer skiff couldn't follow him here; its draft was too deep. He killed the engine, grabbed the beacon and one crate — the lithium cells could be recovered later, if there was a later — and threw himself off the boat onto the flooded platform.

His boots hit concrete, then green-black water up to his knees. He waded forward, the water rising as he went deeper into the station. Behind him, the enforcer skiff idled at the entrance, its spotlight playing across the walls. A figure stood at its bow, scanning with a rifle.

Finn didn't look back. He moved fast, splashing through the tunnels, past the rusted ticket gates and the ghostly remnants of advertising panels. The water was shallower here, only ankle-deep, the station having been partially drained by a collapsed maintenance tunnel years ago. It was a known hiding spot. Also known to the enforcers. He needed to go deeper.

He found the old maintenance ladder and climbed down, into the lower platform level, where the water was waist-high and the darkness was absolute. He stopped, breathing hard, the oilcloth-wrapped beacon clutched against his chest. He listened. Footsteps above, sloshing. A voice. Then another. The enforcers were searching the main concourse. They would check the tunnels eventually, but they'd be slow about it. This wasn't their territory, and they knew it.

Finn moved again, deeper into the lower level, feeling along the tiled wall with his free hand. He knew this station. He'd sheltered here before, during the last purge. There was a signal relay room at the far end, one that the scavengers had stripped bare years ago but that still offered solid walls and a door that could be blocked.

He found it, pushed the door shut behind him, and braced it with a fallen cabinet. The room was dry, protected by a half-fallen wall that had kept the worst of the water out. He slid down to the floor, the crate beside him, and unwrapped the beacon.

It was still blinking. A steady red pulse, patient as a heartbeat. On its casing, in fine white lettering, was a serial number and a calibration date. And a symbol he recognized: the three-barred wave of the Flood Authority's barrier division.

Finn turned it over in his hands. It was light. Plastic and circuitry. It looked like a locator beacon, but it was too small for that, too clean. Maintenance beacons were heavy and rugged. This was something else. Something the high zone didn't want seen.

He heard the enforcers' footsteps recede. They were moving deeper into the station, but away from him, probing the other tunnels. He had time, but not much. The beacon pulsed in his hand, and Finn thought about his father, who had worked on the wall for thirty years before the flood took him. He'd told Finn once that the wall wasn't a wall at all. It was a machine. And every machine had valves. Every machine had parts you could open, if you knew where to look.

The beacon felt like a valve.

Finn tucked it back into the oilcloth, shoved it into his waterproof bag alongside the crate, and listened to the sounds of the enforcers moving through the flood. He could wait here until they gave up. He could wait until dawn, then slip out the eastern vent and make his way home.

Or he could take the beacon to Anya.

Anya, who had made their home in a deconsecrated church, who had salvaged a hundred dead machines and made them sing again, who had the patience to pick a secret apart wire by wire. Anya would know what this was. Anya would know what it meant.

Above him, a shout echoed through the station. Another voice, sharp and commanding. They hadn't found him.

Not yet.