1948: Post-war Britain and an ex-soldier has been found dead with his skull nailed to the floor. Now this case has been re-opened due to media attention and pressure created by his grandson. The killer strikes again and the team discover another linked murder from the 1960s. A further victim is found nailed to the floor - this time in a nursing home for the elderly. Is the Second World War the linking factor? The team must find the next possible victim but no-one knows where he is.
Having established that the killer's victims are the surviving members of the same WWII regiment, Boyd and his team must find the next possible target, but no one knows where he is. The motive for the murders becomes clear when they uncover the story of a brutal gang rape that led to a pregnancy and suicide.
Five-year-old twins Cindy and Jason were abducted in 1988. Sixteen years later, Jason is struck by a car and identified by his DNA after he is admitted to hospital. The hunt now begins to locate Cindy, but Jason cannot recall anything about his life. DS Boyd does not think it is a coincidence when he discovers the driver that struck Jason had crossed paths with the boy shortly before the abduction. Meanwhile, Jason disappears and a police raid in a search for Cindy has tragic results.
The Team effectively proves that dead man was a murder victim, not a suicide and narrows their prime suspects to three inmates at the halfway house where the crime was committed. Two of them have ties to a shady jazz club owner named Phil Brown. After the murder weapon, which is linked to other execution type murders, is stolen from Frankie's lab, Brown is murdered with it.
The body of DS Dave Marvin is found with his throat slashed in a parking lot that has connections to the case. Although there were no signs of sexual activity as in the other cases, someone tried to carve letters into his body but was evidently interrupted. A very embittered Raymond Carstairs reveals that his father, one of the victims, not only was headmaster at a children's school but abused children too, even his own son. Grace suspects that the semen found on the victims may have been purchased on-line. As the case builds to a resolution Bulmer and Boyd clash.
A fourth schizophrenic young woman falls under the spell of the shadowy religious figure known as "The Shepherd," who exploits her paranoia and manipulates her toward murdering psychiatrist Matt Carney, brother of her doctor, David Carney.