St. Peter's Finger (1938)
Surely one of Mitchell's masterpieces (P.D. James, Philip Larkin, and Gladys Mitchell herself thought so): despite Mrs. Bradley's belief that "people nearly always exaggerate when they write or talk about convents," the convent setting is fascinatingly and faithfully described (or at least I imagine so), so that the reader has an impression of seeing the conventual life from behind the scene. The portrayal of the murderess, described as an "embryo saint and martyr", is superb—a fascinating psychological study. The characterisation of all characters is superb—Mrs. Bradley (toned-down without losing force) is not in control—"she had the helpless feeling that, even if she stayed in the convent for the rest of her life ... she would never understand the workings of the minds of the religious, either individually or as a community"—but manages to play the role of devil quite successfully, and her detection is in-depth, competent, and straight-forward, with a reliance on detailed alibi-work. The memorable attacks on Mrs. Bradley; the search on the cliffs; the exploration of guilt, innocence, conscience, redemption, expiation, sin, mercy, and martyrdom; the powerful ending; and the original yet convincing motive, all go to make one of Mitchell's best stories, in which Mitchell succesfully denies the statement that "murder and the conventual life were mutually contradictory".