In the mid 1950’s, one of Scotland’s most notorious killers Peter Manuel brutally murdered several women during a two-year killing spree. Crime-writer Denise Mina unearths the story of a man who killed without conscience and delves into an unusual relationship between Manuel and William Watt, whose family was murdered by the serial killer. In each episode, the writers retrace the steps of the killers and victims, taking viewers through every twist and turn in the story. With unprecedented access to experts, witnesses and journalists that covered each case, the murders are pieced together and new, untested theories surface in attempt to resolve mysteries that remain.