The murder on Nicholas Quinn, a practically deaf secretary of an Oxford institution that conducts examinations abroad. Almost all the supervisors of Quin appear suspicious. Inspector Morse soon discovers that someone is cheating with the exams and that others are giving false alibi's. Another member is killed in the course of the investigation. Morse commits a number of missteps but still manages to unveil the mystery.

The plot is not that strong because first a completely different, acceptable explanation is given by Morse, who then suddenly changes his mind and focuses on someone till then completely unsuspected.