A suicidal man kills several people when he causes a catastrophic train crash, and Sam struggles to cope after one of the young victims dies in his arms.

When a person is found dead in the cells, Sam becomes the main suspect, leaving Ronnie and Wes facing a race against time for them to get their hands on the real culprit.

When the body of a woman is pulled from the Thames after her car is found in suspicious circumstances, the victim's abusive ex-husband seems to be the prime suspect.

Following the suspect death of an old woman, Ronnie and Sam are lead to believe that the old woman's carer was to blame.

A gay father is found beaten to death and the son that he adopted with his partner is missing. In a race against time, Ronnie and Sam go on the hunt for the missing boy.