Boyd and the team take on the task of infiltrating the dark underworld of London's gangland crime families when Harry Newman makes a deathbed confession to 12 "unauthorised killings". Dr Grace Foley is intrigued by this strange expression but Boyd and the rest of the team are tempted to dismiss it as the meanderings of a dying man. Until, that is, forensic psychologist Frankie Wharton discovers that Newman did not die of natural causes, but has been murdered. They soon realise there's a lot more to Newman than they imagined. Added to all that, there's a link to a famous fifties trial in which a gangster was hanged for killing two policemen.

The postliminary inquiries into Harry Newman's past and the identities of the possible twelve murder victims uncover a connection to the infamous trial and execution of a well known gangster.