The Searcher. The Drowned Atlas, #1

The sea rose. The world drowned. People adapted, and lost each other. Wren was one of the four who saved Havenswell: the scout who steered the medicine runners through the storm and came home a hero. But heroes carry private cargo. Hers is a letter, seven years old, folded soft as cloth, written to Rhea, the engineer who was traded to the drowned city's deep-dwellers, who asked Wren to descend with her, and whom Wren, who has never been able to stay anywhere, refused.
Now Wren has learned the truth that broke her heart twice: Rhea surfaced years ago and went searching for her. Two women, circling each other across a drowned ocean. Ships passing. So Wren builds a boat for one purpose and sails into the unmapped margins of a flooded Britain, where stilt-hamlets dwindle on salt-meadows, traders sell hope shaped to your wanting, and no one trusts a lone sail. The search is failing, until a Bridge Folk captain offers a thread: an engineer woman crossed to the Welsh shore, to the lagoon people, and mended what could not be mended.
Behind a fifty-year-old tidal wall, Wren finds the Lagan: a town living on held water and inherited courage, its sluice gate seized, its kelp harvest rotting, its keeper dead with his knowledge half-taught to a daughter who oils his tools and cannot use them. They flinch at Wren's question. They are packing to leave. And on a pump casing in their turbine hall, she finds a repair signed in the one way she would know anywhere: the mark of Rhea's hands.
Then the trail goes suddenly warm, the autumn gales begin to close the one passage south, and Wren, who has spent her whole life running, faces the choice the drowned world has been steering her towards all along. The Searcher is the first novel of The Drowned Atlas, a new series set in the world of Tides of Tomorrow: a story of community, craft, and a love that refuses to stay lost, for readers of Becky Chambers, Station Eleven, and The Light Pirate.
No villains. No despair. Hope, here, is a thing you build.