Tess lives in the “turns”, a network of tunnels under the River Tees, with her Aunt Peg and her monstrous Unkle Darkwater. When Aunt Peg starts to develop signs of dementia, Tess must find someone else to keep her safe. And she is beginning to doubt her aunt's stories about her origins, too. Tess longs to find out the truth about her family once and for all, but that will mean leaving the turns, and she has never been on dry land before – or mingled with dry-folk. Can she survive away from the river? And does she have the strength to take control of who she will become?