Harriet Vane, a crime writer, is charged with poisoning Philip Boyes, her former lover, with arsenic. The evidence against her seems overwhelming, but it is all circumstantial. The jury is divided and a new trial is ordered, to begin in four weeks' time. Wimsey visits Harriet, finds himself falling in love with her, and sets out to clear her name.

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.

Lord Peter asks Miss Murchison to go undercover has a secretary at Norman Urquhart's law firm. She learns he was illegitimate and now paying for a nurse to care for his mother. Insp. Parker confirms Philip Boyes was definitely poisoned.

Lord Peter asks his secretary Miss Climpson to find out what Urquhart's nurse Miss Booth knows. Faking a seance Miss Booth admits that Urquhart has forged Philip Boyes Will to make him the sole beneficiary but can Lord Peter break him.

Mrs. Weldon says she intended to marry dancer Paul Alexis and believes he was murdered. Lord Peter tells journalist Salcombe Hardy that the owner of the razor was the murderer. Peter and Harriet attempt to recreate Alexis last movements.

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.

While on a walking tour of the West Country, Harriet stumbles on the body of a bearded man with his throat cut on a rocky outcropping near the sea.

Old Pollock tells the police he sold Paul Alexis 300 gold sovereigns. Lord Peter and Harriet attempt to deal with his infatuation and her fragile state of mind. Looking for Mrs. Weldon's husband, Bunter has more questions than answers.

Peter and Harriet solve Paul Alexis coded letter and learn he was plotting to restore the monarchy to Russia. However his arranged meeting took place two hours before he died and witness Jem Pollock only saw Alexis meet with a young woman.