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 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?

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?