Years after her mother vanished, Sam Gillingham wants answers. Her mother's secluded life leaves room for few leads, but an unsettling clue emerges.
Sam details her parents' unusual living arrangement. In 1993, Russell goes yachting with friends and has a peculiar episode at sea.
Mark confronts Patricia about her old work permit. In the 1990s, a national publicity campaign prompts new witnesses to come forward.
Mark speaks with a police officer about the plausibility of Russell's claims, but a few final letters from Russell suddenly complicate matters.
Mark investigates the disappearance of Eastbourne teen Louise Kay, but a crucial revelation about a notorious suspect redefines the scope of the case.
As the complex search for answers evolves, Mark travels to Glasgow and unpacks the chilling murders of Anna Kenny, Agnes Cooney and Hilda McAuley.
Mark's efforts lead to one final murder case, which threatens to derail his theory about two heinous suspects with similarly volatile histories.