Inspector Hanaud, the well-known French detective, is on holiday in Aix les Bains when he is asked by a young Englishman, Harry Wethermill, to investigate the murder of a wealthy widow, Mme Dauvray.

Mme Dauvray had been fascinated by spiritualism and part of Celia’s role as companion had been to stage séances for her and, as a supposed medium, to conjure up manifestations from the spirit world - which she did by acting and trickery.

In league with Hélène Vauquier, she professes disbelief in spiritualism and goads the old lady into holding a séance in which Celia will be expected to perform while bound hand and foot.

Visiting a hotel in Richmond, Mason's attention was drawn to two names that had been scratched by a diamond ring in a window pane: Madame Fougère, a wealthy woman who had been murdered the year before at Aix les Bains, and that of her maid who had been found bound and chloroformed in her bed.

[4] However, in their 1989 A Catalogue of Crime Barzun and Taylor were more critical; they called the characters 'cardboard' and felt that the author's skill in plotting and telling did not compensate for the book's period faults.

[5] Writing in 2017, Martin Edwards called At the Villa Rose “a landmark of the genre” in which real-life source material is blended with phoney spiritualism, baffling but logical detective work, and an unexpected villain.

[6] Its main flaw, he thought, was a lopsided story structure in which the murderer is revealed part way through the novel, with the later chapters amounting to an extended flashback.

[4] Mason's stage version of the novel, also called At the Villa Rose, opened at the Strand Theatre, London, on 10 July 1920, with Arthur Bourchier in the role of Hanaud, Kyrle Bellew as Celia [sic] and Harcourt Williams as Wethermill.