The 21 Killer, a case from Rick Bentz's past, comes back to haunt him. Twin sisters have disappeared again.

"He's a serial killer. A murderer of young women, all killed in brutal attacks. But despite Hamish Wolfe's conviction, he's always stuck to his story -- he's innocent and he's been wrongly imprisoned. And now he wants someone to investigate and, more importantly, to write his story. Maggie Rose is a notorious defense attorney and writer whose specialty is getting convictions overturned. At first, Maggie is reluctant to even acknowledge Hamish's requests...

While visiting his family in Cornwall, Private Detective Cormoran Strike agrees to take on a cold case involving a woman who went missing in mysterious circumstances in 1974, and as Strike and his partner in the agency, Robin Ellacott, investigate the disappearance, they come up against a fiendishly complex case with leads that include tarot cards, a psychopathic serial killer, and witnesses who cannot all be trusted.