"I saw a child killed... He was strangled upstairs, right by the horse." Billy has obvious mental health problems, but he is sure that he saw the murder of a child as a child - and a long-standing alarm finally leads him to the office of private detective Cormoran Strike, who became famous again after the capture of the Shacklewell Ripper. Billy does not have time to finish, frightened by the prospect of an imminent arrival of the police, but his story does not get out of Strike's head.