When the police find other cases of people who vanished into thin air, they begin to think they may have a serial killer on their hands. They arrest Tom Franke, seen on CCTV footage as a regular at the Covent Garden market where Harrington disappeared. He doesn't fit the pattern of a serial killer but Walker isn't prepared to rule him out. When the police broadcast his image and asking for anyone who might know him to get in touch, Franke sets out to take advantage of a still frantic Susan Harrington. He lures her to a meeting with a promise to bring her to her husband, but he's not as clever as he thinks and is soon arrested and charged with murder. The principal questions at his trial are about the perpetrator's mental health and whether he is 'mad' or 'bad'.