Harriet Vane attends a reunion at her Oxford College and is asked by the Warden to investigate a series of poison pen notes that several members of staff have received. She takes up residence in the college and receives one of these notes herself. In the cloistered environment of the school, there is any number of possible suspects. In the absence of a motive however, it is difficult to determine if the culprit is a member of staff, a student or even if it is a man or a woman. When Lord Peter Wimsey visits the college - as much to see Harriet as for anything else - he agrees to assist in the investigation. What he finds is that one member of the staff had reason to seek vengeance.

Harriet Vane continues her research into the odd goings on her old college. She is attacked and knocked unconscious while investigating someone playing the organ in the college chapel in the middle of the night.

The prowler evades Harriet but leaves hairpin. Peter is asked to look over the evidence but Harriet is left flat when he follows an inquiry without her. Miss Devine's tale of an academic faking his thesis points to someone with a grudge.