Gethk looks as if the river has been slowly editing him. His olive-brown skin is stippled with pale freckles from years of reflected sunlight, and his dark hair is bound in a short tail with a bit of surveyor's cord. He moves with a careful, side-stepping gait, testing boards and stone with his boot before trusting them. In a crowded room, his eyes go first to thresholds, windows, and the line where floor meets wall, as if mapping a route out. A detail that catches people off guard: he keeps a tiny paper theater folded in his coat and unfolds it for children while waiting for a ferry.

Gethk is hopeful enough to make plans after disaster, but wry enough to distrust anyone who calls a plan foolproof. With strangers he is brisk and exact, measuring every promise against the terrain; with frightened people he becomes patient and unexpectedly gentle. When angered, he does not flare up. He starts naming consequences, one by one, until the room understands the danger.

Gethk grew up in a dry quarter of the river city, where his mother copied property boundaries for a magistrate and his father ferried people through the old canals. When a spring flood broke the southern gates, Gethk was seventeen and carrying a survey chain for a crew sent to mark safe roads. He found a schoolhouse trapped behind a collapsed sluice and disobeyed orders to retreat, guiding its pupils over rooftops by chalking arrows on chimneys. The city later praised his map, but his father drowned ferrying the last families out. Gethk still believes a good map is a promise that somebody will come back for you. He now charts shifting channels, submerged streets, and buildings that disappear below the waterline. He trades field notes with Nali, a patient ferry pilot who distrusts his shortcuts, and owes the roof-repairer Bwana a favor for sheltering refugees in a half-sunken bell tower. His former employer, the municipal survey office, wants him to certify a new flood barrier as safe. Gethk has found evidence that its foundations are already failing, and the official who commissioned it is pressuring him to keep quiet.