Thinwater - C. M. Wilder

Dan Mercer used to run toward danger for a living. Then burnout took his home, his rhythm, and everything he thought made him useful. Now he lives on a narrowboat on Birmingham's canals, keeping his world small and quiet, until the canal starts knocking back.

When nine-year-old Ellie Parker vanishes under a bridge, the official story is simple: accident. Dan knows it's a lie. The water doesn't behave like a drowning. The echoes don't behave like echoes. And a sleek business card from Glass & Co. suggests the city's "infrastructure" runs deeper than concrete and steel.

As secret Wardens move to contain the truth and a corporate Fae court begins testing the boundary, Dan is forced into a bargain he doesn't want and a war he didn't know existed. Because in a city of thresholds, someone always pays. And Dan refuses to let it be a child.