A detective team apply new techniques to old crimes as they solve cold cases.
A young woman, Marina sets fire to an abandoned car in a street and takes photographs of it as it burns. Boyd walks by and tackles her to the ground, attempting to shield her from the possible explosion. He later learns that Marina's father died in a car accident a few years earlier in that spot, and Marina refuses to accept that his death was an accident. Although not officially a cold case, Boyd is intrigued and reluctantly agrees to investigate. Frankie runs forensic tests on Marina's father's car and proves that he was still alive after the crash and could have escaped. The answers they uncover may mean that the danger to Marina is much greater than any of them had suspected.
Boyd has Marinas uncle, Mike Coleman and her mother Gwen brought in for questioning while Frankie searches the house. The team find the items that were recovered from the car nine years ago and suspect that Perry Coleman was being blackmailed by Rod Brogan, a friend of Perry's. Boyd has the body exhumed and the DNA results surprise everyone.
Workmen are burrowing in the crypt of a Catholic church when they come across the skeletal remains of a young man buried in concrete. The squad sets about trying to pinpoint the identity of the body, which was buried with the accoutrements of certain Catholic rituals. Even more oddly, there is a message in Braille buried with the corpse, which tums out to be a passage from one of St Paul's letters to the Corinthians The team suspects that the body was never meant to be discovered.
The hunt continues for the murderer. The team uncovers some long hidden family secrets while questioning the community & congregation. Also Frankie discovers a possible biological connection between the former parish priest, Father Stuart, and the first victim.
Boyd and the team decide to reopen the 25 year old case of Annie Keel, a woman who was tried and convicted of a double homicide solely based upon her own confession. Boyd doubts the validity of the conviction, and decides to dig deeper to possibly discover what really happened. Why did Annie confess? Did she really commit murder, or was she covering for someone else?
Boyd and the team continue their investigation of the Annie Keel case, and try to locate her son who was present during the murders.
When the corpse of a well-known police woman who went missing a year earlier is found floating in the Thames, Boyd and his team of investigators try to track down who murdered her and her unborn child.
Grace is not convinced that the stalker who confessed to the murder is truly guilty. But who really killed the police officer? Was it possibly the stalker, her ex-husband, or the married father of her unborn baby?
