Boyd's team are sure the dark figure cited by two homicidal psychiatric patients exists, and continue to investigate the mysterious Shepherd.

A woman torches her home, killing her family. She claims that she was incited to commit arson by a mysterious figure called 'The Shepherd'.

The cold case team continues to try to unravel the macabre murders, and DNA evidence brings them towards their suspect.

A man is found dead at a hotel with a word carved into his back, the hallmark of an old crime that the cold case team is already investigating.

The secret past of the team's guitar teacher suspect is revealed, and Frankie is embarrassed following the attack on the lab.

Sam Jacobs is released from prison to start a new life. When a man is murdered in his hostel, he becomes a suspect - but he may have been the intended victim.

Mel is suspended from the case pending an inquiry, while Grace and Boyd have more questions for Roper, but the doctor is in no position to answer them.

A man is admitted to hospital 15 years after he and his twin went missing from their home. Before he can be interviewed, a murder takes place and he goes missing once more.

An ex-army officer who served in Northern Ireland's Troubles points Boyd's suspicions towards the security services, making the case more complicated than ever.

Who is the skeletal inhabitant of a car abandoned in a disused garage, and what links him to the assassination of a government minister 25 years ago?

The team know what links the victims but they are still searching for the motive - and for the murderer.

A common theme, linking three murders over a 60 year period, is discovered when the case of the murder of an ex-soldier is reopened. Can the team prevent a fourth killing?