First published: UK, Michael Joseph, 1938
Surely one of Mitchell’s masterpieces (P.D. James, Philip Larkin, and Gladys Mitchell herself thought so). Mrs. Bradley believes that “people nearly always exaggerate when they write or talk about convents”, but 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 killer’s character is a fascinating psychological study. The characterisation of all characters is superb. For once, 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 successfully denies the statement that “murder and the conventual life were mutually contradictory”.
Times Literary Supplement (Maurice Percy Ashley, 24th September 1938):
Here are four detective stories  any of which would have stood at the top of the list in the dog days. An order of preference is largely a matter of taste, but many regular readers of detective stories will particularly appreciate Miss Mitchell’s new book because it has all those qualities which are conspicuously absent from the inferior type of thriller. The narrative has unity, the characters are real and the setting in a convent school and orphanage is distinctive without being fantastic. In tune with her temporary surroundings Miss Mitchell’s detective, Mrs. Bradley, is more sympathetic than in her previous adventures. Previously this little woman, with her sharp tongue and irritating cackle, has been pictured as the sort of person who discusses birth control and Fascism at Left-wing cocktail parties. But in investigating the murder in the convent she is entirely respectable and even amiable.
 The other three are Too Many Cooks by Rex Stout, Death in Five Boxes by Carter Dickson, and Such Natural Deaths by Lindsay Anson.
A child in the convent school has been found submerged in a bath, not drowned but poisoned by gas. The geyser is discovered in perfect order and for some obscure reason the coroner permits a verdict of suicide. The nuns invite Mrs. Bradley to investigate, and she interviews all the religious and lay sisters, the children at the private boarding school and the orphans who do the domestic work. Although the characters are many, they are all distinct, and the number of suspects is obviously limited. Except for the introduction of one or two pretty obvious red herrings, Miss Mitchell plays perfectly fair with her readers, but it would have been easier to work out the actual circumstances of the crime if she had appended a sketch-map of the buildings.
Manchester Guardian (E.R. Punshon, 30th September 1938):
Miss Gladys Mitchell’s St. Peter’s Finger may be adjudged more successful in its description of convent life than it its strictly detective interest. The nuns, their pupils, the orphans in their charge are drawn with sympathy and insight, and a real impression is conveyed of the busy, eventful peace of convent life. Annie, the industrious, one of the orphans, is a mistress’s dream; and Bessie, another orphan, with her good heart and her ambition to be a gangster queen, is a sheer delight. One of the pupils at the convent school has been found dead in a bath; Mrs. Bradley, a much tamed Mrs. Bradley whose crocodile smile is now all sweetness and light, is called in and discovers the truth. But her conclusions seem to be arrived at largely by guesswork, there is little to show that they are correct, and too many of her activities have the air of being designed merely to deceive the reader. Maxim: Readers should not be deceived, they should be lovingly induced to deceive themselves.
Spectator (Nicholas Blake, 30th September 1938):
St. Peter’s Finger opens very nicely with a young girl gassed in a convent. The scene enables Mrs. Bradley to exercise all her insidious charm and outrageous unconventionality, though she finds the passive resistance of the nuns a very hard nut to crack. The problem set the reader is an interesting one (a minor problem is to discover the relevance of some of the chapter-headings, which are of a fearful reconditeness), but I found it difficult to keep all the threads of the plot in my hand, and it does peter out a little towards the end: perhaps this is because the criminal’s motive strained my credulity.
Observer (Torquemada, 2nd October 1938):
Gladys Mitchell is to be sincerely congratulated on her latest and very readable detective novel, St. Peter’s Finger, even though she is guilty in it of a little backsliding, and does not so criminally satisfy us as she did in Come Away, Death, and even leaves us with a sense of incompletion, as she did in Dead Men’s Morris. After covering a great deal of ground and giving us more than one kind of mystery in her Greek excursion, she now shows that she can take an even longer spiritual round in the small space of a single convent. A little girl is found gassed in a bath where she has no business to be; a most naturally subdued Mrs. Bradley is called in by the nuns to investigate; thereafter we live with the sisters and the orphans in an appealing intimacy. That Gladys Mitchell, during a splendid piece of local reconstruction, opens our minds to minor doubts (as when she attributes buttocks to Leviathan, and—“it wouldn’t have done for the Duke”—some fine and sprightly lines from Tennyson’s “Sir Galahad” to the same author’s “Ode on the Death of the Duke of Wellington”) does not spoil our pleasure in very clever work: but when she expects too much of our intellect and demands that we should be satisfied with a doubtful conversation held during the horrors of a fire, and an incomplete motive, and a slurred method, she a little jeopardises her position as one of the Big Three women detective writers.
The Times (4th October 1938):
THE PATTERN OF THE PUZZLE
The immense number of detective stories published has led authors far afield in the search for original plots. There is danger here. In this search for an astonishing solution it is a mistake to astonish the reader too much. Once reason rebels the author is lost. The latter therefore must always be careful not to let plausibility be obscured by extravagance; and, in the pattern of the puzzle, every small piece must slip neatly and inevitably into place.
How regrettable then that a writer of the charm and ability of Miss Gladys Mitchell should propound a solution to her latest murder that is beyond belief. Up to this point, St. Peter’s Finger is an admirably constructed story lifted out of the ordinary by its setting and characterisation. The mystery is the death of a child in a bathroom ostensibly by accidental gas poisoning, although it is obvious that this is too simple a solution to the problem; the background, depicted with skill and fidelity, an English convent school. Until the closing chapters the reader is happily carried along, amused, intrigued, and satisfied; but with the dénouement he is left asking himself—and the author—almost as many questions as did Mrs. Bradley in the course of her investigations.
John O’London’s Weekly (Anthony Berkeley, 7th October 1938):
A new book by Miss Gladys Mitchell has always been a delight, and now that she has toned down a one-time tendency to excessive elusiveness the delight is intensified. Mrs. Bradley is as clever a creation as has ever been devised, combining as she does the eccentricity and odd characteristics considered indispensable in the private detective of fiction with a rounded reality shared by few others. It gives this reviewer at any rate a positive thrill of pleasure to encounter again her cackles and her yellow claw. In St. Peter’s Finger she is at the top of her form in a convent—if you can imagine Mrs. Bradley in a convent. Here Miss Mitchell has scope for her genius for settings, and one might imagine that she must at one time have taken the veil herself, so detailed is her knowledge of convent life, habits and characters. The problem of the death of a small girl from carbon monoxide poisoning in a guest-house bath is ingenious, and it is still more ingeniously complicated by a factor which must not be divulged. A decorously riotous entertainment.
New Statesman (Ralph Partridge, 8th October 1938):
Only the Gladys Mitchell continues to disappoint me; but I have never been partial to the Lizard Lady, whose luxuriant rambling habit never seems justified by the rather insignificant sallow fruit…
Miss Mitchell’s Mrs. Bradley penetrates into a nunnery into St. Peter’s Finger and subjects all the nuns to her basilisk scrutiny. A little girl attending the nunnery school is found dead in a bath, not drowned but gassed, yet the geyser is in perfect order. I am reluctantly compelled to believe that Miss Mitchell only launches Mrs. Bradley on these detective jobs in order to indulge her inordinate desire to pry into people’s private lives and set them to rights, not to solve crimes for the public weal, because the final explanation of the technique of the criminal in St. Peter’s Finger is beyond all plausibility.