The Lake District's cold case specialist, DCI Hannah Scarlett, is determined to uncover the truth behind Bethany Friend's apparent suicide in the Serpent Pool. Why would Bethany, so afraid of water, drown herself? Hannah fears that her partner, bookseller Marc Amos, is keeping dark secrets. Does he hold the key to Bethany's past - and why was his best customer burnt to death in an Ullswater boathouse?

Hannah still carries a torch for Daniel Kind, who is researching Thomas De Quincey and the history of murder. Once Daniel and Hannah suspect connections between Bethany's drowning and a current sequence of killings, death comes dangerously close to home.