Despite the dons' reluctance to share the secret with an outsider, Harriet convinces them to let her bring in Lord Peter Wimsey to assist the investigation – but his involvement is not without complications, both personal and professional.

Expecting hostility because of her notoriety (she had stood trial for murder in an earlier novel, Strong Poison), she is surprised to be welcomed warmly by most of the dons, and rediscovers her old love of academic life.

Harriet, herself a victim of poison-pen letters since her trial, reluctantly agrees, and returns to spend some months in residence, ostensibly to do research on Sheridan Le Fanu and to assist a don with her book.

The timing of the first poison pen message during the gaudy, and the use of a Latin quotation from the Aeneid during one disturbance, focuses suspicion on the Senior Common Room dons, causing escalating tensions.

As Harriet wrestles with the case, trying to narrow down the list of suspects who might be responsible for poison-pen messages, obscene graffiti, wanton vandalism including the destruction of a set of scholarly proofs, and the crafting of vile effigies, she is forced to examine her ambivalent feelings about Wimsey, love and marriage, and her attraction to academia as an intellectual and emotional refuge.

[3] Writing in 1936, George Orwell disagreed with the opinion of an Observer critic who felt that Gaudy Night had put Miss Sayers "definitely among the great writers".

Harriet Vane and Saint-George, the undergraduate nephew of Lord Peter, help give variety, and the college setting justifies good intellectual debate.

The narrative is interwoven with a love story and an examination of women's struggles to enlarge their roles and achieve some independence within the social climate of 1930s England, and the novel has been described as "the first feminist mystery novel".