The Met is trialing an unsolved cases squad, with DCI Peter Boyd in charge. Boyd chooses one of his own cases, teenager Alice Miller was kidnapped, raped, and murdered 5 years ago, and Boyd will not fail her again.
A newly discovered note seems to set the seal on a suicide verdict, but when Boyd and the team exhume Perry Coleman's body, DNA tests reveal some disturbing facts.
An anonymous letter writer demonstrates to the Boyd that Annie Keel was not the only person present during the murders, but his motivation remains a mystery.
The body of missing Police Sergeant Debbie Briton turns up in a golf bag. Suspicion falls on a stalker, but Grace is not convinced that he is the killer.
Boyd and the team track down murdered police officer Debbie's married lover, but he denies killing her. Meanwhile, stalker Christopher Redford is ready to confess to the murder, but Grace is not convinced he's the guilty man.