Tony's patient, the child killer Maggie, is on the verge of revealing where she buried her victims, but Tony and the police are distracted by a serial murder case involving the roommate of one of his students.

Newly promoted to Detective Chief Inspector, Carol investigates a murder which seems to bear the hallmark of gang boss Gavin Cochran. However Cochran is behind bars for murder and could not have done it. Carol asks Tony to work out any links between the two slayings, leading to the arrest of Cochran's brother George. But there is a fight during which George ends up in a coma. Gavin is released from prison for a compassionate visit, during which another killing takes place, allowing Tony to test his theory and trap the murderer.

The suspicious death of a hospital patient leads to post mortems being conducted on other patients who supposedly died of natural causes but now appear to have been murdered. Tony suspects the killer may be a person who believes they are releasing the victims from pain by their actions, guided by religious motives. However Islamic terrorists are also suspected, leading to the involvement of MI5. Carol is under scrutiny and needs Tony's help to keep her job.