The private investigator Cormoran Strike is in Cornwall, visiting his family, when a woman approaches him asking for help in finding her mother, Margot Bamborough, who disappeared under mysterious circumstances in 1974. Strike has never dealt with an unsolved case before, but despite having little chance of success, he agrees to take it on.

At the same time, his partner, Robin Ellacott, is trying to balance a difficult divorce with her feelings for Strike. As Strike and Robin investigate Margot's disappearance, they face a series of complex clues such as tarot cards, a psychopathic serial killer, and unreliable witnesses. They will realize that even old cases can prove deadly...