Read Chapter 23: The Last Chart Puzzle

The air in the mill's upper floor was thick with the smell of wet wool and drying mud. Finn sat with his back against a rusted beam, Tess beside him, her fingers tracing the lines of the damaged chart spread across her knees. His arm throbbed beneath the bandage, and the fever had begun to make the edges of the room swim.

Danny came up the ladder without a sound. Finn saw him first, and the man's face—usually cracked with a grin—was stripped bare. He looked at Finn, then at Tess, and something in his posture shifted, like a man setting down a weight he'd carried for years.

"Boatman," Danny said. "We need to talk."

What he said next made the stillness of the mill feel deeper, colder.

"I wasn't just a courier for the scavengers." Danny's voice was low, barely audible over the wind rattling the broken windows. "I was placed in the low zone five years ago. Undercover. Reporting to a faction inside the high-zone administration that opposes the official."

Finn's hand slid toward the knife at his belt, but Danny raised both palms. "I know what that sounds like. And I'm not asking you to trust me. But I've been feeding you the truth the whole way, and I told you once that no chart I carried would ever sell you out. That's still the truth."

"He's the spy Anya lost," Tess said quietly, not asking. Her eyes were hard.

Danny nodded. "My channel went dark when they swept the maintenance tunnels. I barely got out."

Finn stared at him. He thought of the routes Danny had given him in the first days—the way Danny had known the backchannels like he'd grown up in them, because he had. He'd been born in the low zone, before the walls went up. He'd watched his mother be refused a medical node for six hours while she bled out from a wound the high-zone could have treated in minutes. That kind of grief didn't fake well.

"Who do you work for?" Finn asked.

"I can't give you names," Danny said. "They put families in the line if I do. But they're engineers. Hydraulicists. The same people who designed the barrier system—the people who know the official's plan is murder, not infrastructure."

He pulled a folded sheet from his coat. The paper was dry, laminated, the markings in precise red and black ink. He laid it over the water-damaged chart, his finger resting on a point where the main barrier wall curved inward, a place where the structure had been built over older foundations.

"Node nine-seven-delta," Danny said. "There's a weakness there. A joint between the old Thames Barrier segments and the new wall. It was never meant to hold the pressure of a full-system event. If you plant charges there and detonate at low tide, the wall will crack."

Finn's eyes moved between the chart and Danny's face. "And then?"

"The entire barrier system has fail-safes tied to structural integrity. If the main wall blows, the system will be forced to open all locks to equalize pressure—or risk losing the whole wall and flooding even the high zones." Danny paused. "It saves the low zone. It saves everyone."

There was another piece to it. Finn could see it in the way Danny wouldn't quite hold his gaze. He waited.

"The wave," Danny said at last. "You detonate at low tide, but you're still introducing a pressure spike. The water that comes through won't just rise—it'll surge. The lower districts of the high zone sit at only four meters above mean. That wave would take out the processing sectors, the habitation blocks nearest the wall. Thousands. Maybe tens of thousands."

Silence stretched across the floor. Outside, some scavenger's child cried out in a dream, and the sound was painfully ordinary, a piece of the world that hadn't yet caught up to the weight of Danny's words.

Tess looked at the chart, then at Finn. Her jaw was tight. She said nothing, but her hand moved to rest on his forearm—a touch that said what her voice wouldn't: don't make this choice alone.

"How do we know it works?" Finn asked. "That the fail-safes will trigger, not just double-lock?"

Danny shook his head. "We don't. The engineers think it's an eighty-percent chance. The official thinks the wall can take anything, which is why he's pushing to seal the low zone while the pressure is still low. He's assuming the fail-safes will hold if anything goes wrong. That assumption is the only opening we have."

Finn looked down at his own hands. They were shaking, and not just from the fever. He'd seen the dead this week. Enough of them. He had carried a child out of the water—Anya's boy, spluttering, alive by a meter of luck. He had watched people he knew drown in the flooding of their own homes, bodies folding into the current like they were nothing, like the water had always owned them.

He'd killed men before the flood, too, on the canals when the code of the water demanded it. He knew what weight a life had, what it could bear. He had never been asked to hold ten thousand of them at once, ask them to die so that his own people could have a chance to live.

"What does the official do with them?" he asked. "What does he tell the survivors?"

Danny grimaced. "The plan is called 'managed collapse.' They'll stop supplying the remaining nodes, close out the water pipes, let the district slowly die of exposure and starvation. Then they'll repurpose the zone as a thermal sink for the core's new servers. It gets erased completely. To them, it's not even a district. Just a shallow bit of land under a wall that was always meant to be replaced."

Finn stared at his hands again. The pain in his arm was sharp, hot, digging at him like it was trying to tell him something he didn't want to hear. He was running out of time. The whole district was.

"Danny," he said. "If I plant that charge, I'm not killing high-zone citizens. I'm killing the same people who have been selling us half-rations for years, holding our flood gates open while the core gets first water every time. I've lost three friends in a week to the men in white armor. I'm not afraid of that weight."

Danny waited, his eyes steady.

Finn touched the point on the chart—Node nine-seven-delta. A place where the water and the wall met, and where everything might bend, one way or the other.

"Take me there," he said.

The reversal hit him before Danny could answer. Through the floor of the mill, through the iron bones of the old building, came a deep, hollow thrum. It wasn't thunder. It was water—a dense, moving mass of it, coursing through the sealed channels beneath the city.

Low tide was still hours away. But the floodgates were opening anyway.