"An unusual and challenging puzzle mystery that will keep [you] guessing until the final pages. Wow!" —Library Journal STARRED review

Seven years ago, Bethany Friend was found drowned in mere inches of water in the lonely Serpent Pool in England's Lake District. Was it suicide or murder? Now, determined to win justice for Bethany's dying mother, DCI Hannah Scarlett of the Cold Case Squad re-opens the case.

But Hannah has problems of her own: a new sergeant with a reputation for causing trouble, a new house close to the Serpent Pool, and new cause to doubt her partner, second-hand bookseller Marc Amos. Worried by dwindling finances and the horrific death of one of his best customers, Marc finds himself drawn to the lovely and enigmatic Cassie Weston, who works in his shop.

Then Hannah meets Louise Kind, sister of historian Daniel Kind. Louise has been living with book collector and lawyer Stuart Wagg, and has just confessed to her brother that she struck Wagg with a knife. Searching for the supposed victim, Hannah and Daniel—who is writing a book about the brilliant but opium-addicted 19th-century English writer Thomas De Quincey—encounter dark secrets and strange obsessions that oddly echo De Quincey's drug-fueled writings.