The Crime: Customers of a convenience store are taken captive. The Demand: The man needs to know what really happened to his son, who died an "accidental" death in prison. The Twist: What Detective Tom Thorne discovers upends everything he thought he knew about those he put away. But will it be enough to fulfill the wishes of the distraught and dangerous father?

A murderer is targeting the children of victims of Raymond Garvey, an infamous serial killer from London's past. When Murder Squad veteran Detective Tom Thorne is called into what seems like, for once, an ordinary domestic murder, he thinks he's caught a break. But when a mysterious sliver of bloodstained X-ray that was found clutched in the victim's fist is replicated at other crime scenes around the city, Thorne realizes this is not a simple case.