Troubled Blood by Robert Galbraith

Second Hand 

In the epic fifth installment in this "compulsively readable" (People) series, Galbraith's "irresistible hero and heroine" (USA Today) take on the decades-old cold case of a missing doctor, one which may be their grisliest yet.

Private Detective Cormoran Strike is visiting his family in Cornwall when he is approached by a woman asking for help finding her mother, Margot Bamborough--who went missing in mysterious circumstances in 1974.

Strike has never tackled a cold case before, let alone one forty years old. But despite the slim chance of success, he is intrigued and takes it on; adding to the long list of cases that he and his partner in the agency, Robin Ellacott, are currently working on. And Robin herself is also juggling a messy divorce and unwanted male attention, as well as battling her own feelings about Strike.
As Strike and Robin investigate Margot's 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. And they learn that even cases decades old can prove to be deadly . . .