Although DC Morse has been assigned to general duties, he takes an interest in the murder of Evelyne Balfour, a barmaid who was strangled to death and found in an abandoned rail car. DI Thursday is certain she had been stepping out on her husband but a second murder - that of Grace Madison - leads them to believe they are dealing with a serial killer. At both crime scenes, Morse finds that the killer has scrawled a phrase from a classic opera. Mrs. Madison had an appointment with a Mr. Nimmo who is, according to a neighbor, an opera lover. They eventually find Ben Nimmo dead, buried alive, again in a manner described in the opera Aida. They also find Morse's photo on the wall. Psychiatrist Dr. Daniel Cronyn suggests it may be a former patient, Keith Miller and Morse thinks he's found a pattern to the murders.
—garykmcd