Lacey Flint, Sharon Bolton's enigmatic protagonist, has been living in a houseboat on the River Thames, and she's becoming a part of London's weird and wonderful riverboat community. Against her friends' better judgment, she's taken up swimming in the Thames, and she feels closer than ever to Detective Mark Joesbury, despite his involvement in a complicated undercover case. For the first time in her life, as she recovers from the trauma of the last few months, Lacey begins to feel almost happy.

Then, at dawn one hot summer morning while swimming down the river, Lacey finds the body of a...