Peter Manuel, recently released from a nine-year prison term for a series of sexual assaults, is determined to make Detective William Muncie - the man responsible for his incarceration - pay the price. After a further sexual attack on a young woman named Mary McLauchlan, Manuel elects to defend himself in court and manages to secure a not-proven verdict. Muncie promises a distraught Mary that he will not rest until Manuel is behind bars.

Nine months after the death of Anne Kneilands, the police are no further forward in finding her killer, although Detective William Muncie is sure he knows the culprit. Even though not part of the investigation, he goes to Peter Manuel's home to try and reason with his father who gave him the alibi he needed to be free from police suspicion. Then Muncie hears the news that three women in the Watt family have been shot dead in their beds. The husband William, who was on a fishing trip at the time, is arrested. However, Muncie is convinced Manuel is the man behind all four murders.

In the final episode, a search operation is organised with local volunteers scouring the countryside in search of missing girl Isabelle. Eventually her coat is discovered and identified by her distraught mother. In the early hours of New Year's Day, the Smart family - Peter, Doris and 12-year-old Michael - are all shot dead in their beds. Muncie puts Manuel under 24-hour watch and enlists the help of ex-con Joe Brannon. Finally Muncie has a breakthrough, recalling that Peter Smart's wallet at the crime scene was empty of cash. Brannon confirms that on New Year's Day, Manuel was spending cash like water and buying rounds with brand new one-pound notes. The bank confirms that Peter did withdraw cash on New Year's Eve - 15 pounds in new notes. Manuel is arrested and Muncie has him where he wants him, as he tries to get Manuel to admit his crimes.