Someone at Oxford's Foreign Examination Syndicate is selling exam secrets. Nicholas Quinn, a member of the board, overhears something he shouldn't know about and is soon found dead at his cottage, poisoned with cyanide - but Nicholas was deaf. Then crossword compiler Philip Ogleby has his skull smashed in. During his investigations, Morse is attracted to Monica Height. She works for the Syndicate and may be mixed up in the corruption which led to Quinn's murder, and perhaps to Ogleby's as well.

Morse is passed over for promotion and gets a new working partner in the shape of Lewis, who is not sure what to make of his new boss. Their first case together is a murder, when Anne Staveley, who was Morse's friend in a choral society, is found hanged in her house in the Jericho area of Oxford. The death looks like suicide, but Morse has his own reasons for treating the case as a murder investigation. A parking ticket and Oedipus the King, by Sophocles, come to his assistance.

Morse investigates murder on hallowed ground. A quiet country church is an unlikely setting for the killing, and a vicar and his voluntary helpers are the unlikely suspects. Among them is Ruth Rawlinson, whom Morse is attracted to. Then it appears that a serial killer is at work.