Treason in My Breast is a 1938 mystery detective novel by Anthony Gilbert, the pen name of British writer Lucy Beatrice Malleson.

[1][2] It is the fourth in her long-running series featuring the unscrupulous London solicitor and detective Arthur Crook.

[3] Crook became one of the established characters of the Golden Age of Detective Fiction, although in this case the novel was more similar to a Victorian melodrama than a conventional whodunnit.

From her window, a housewife believes she has witnessed the build-up to a murder of a young woman in the flat opposite.

She calls in Arthur Crook to assist her in unravelling what seems to be an ingenious attempt to steal a large inheritance.