When Billy, a troubled young man, comes to private eye Cormoran Strike's office to ask for his help investigating a crime he thinks he witnessed as a child, Strike is left deeply unsettled. While Billy is obviously mentally distressed and cannot remember many concrete details, there is something sincere about him and his story.

Strike and Robin set off on a twisting trail that leads them through the backstreets of London, into a secretive inner sanctum within Parliament and to a beautiful but sinister manor house deep in the countryside.