Monsieur Ricardo a l'habitude de passer ses vacances dans la tranquille station thermale d'Aix-les-Bains. Il aime jouer au baccara à la Villa des Fleurs ou flâner dans les jardins et observer les joueurs. Mais, dans ce haut lieu de villégiature de l'aristocratie, se trame un complot savamment organisé. Entre cures thermales et tables de jeu, se tissent des liens qui aboutiront à un crime crapuleux et, au premier abord, inexplicable.

In 1910, Mason undertook to create a fictional detective as different as possible from Sherlock Holmes, who had recently been resuscitated after his supposed death by Arthur Conan Doyle in 1903. Inspector Gabriel Hanaud was stout, not gaunt like Holmes; a professional policeman, not a gentleman amateur; from the French surete, not Victorian England; and relying on psychological insights rather than physical evidence. His "Watson" is a retired London banker named Mr. Julius Ricardo.Hanaud's appearance in the 1910 novel, At The Villa Rose marks "the first major fiction detective of the Twentieth Century," according to a historian of the genre. Set in the south of France, its plot also ridicules spiritualism and mediums, well-known enthusiasms of A. Conan Doyle.Four more Hanaud novels and several short stories followed, the last, The House in Lordship Lane, in 1946 and the only one set in England.The first Hanaud book was a best-seller, as were several of his 20 novels, and as such often adapted into films, often more than once. A 1920 version of At the Villa Rose was a great success in British movie theaters that year, even as a play version of the novel simultaneously began a long run at the Strand. A successful silent version of The Four Feathers followed the next year.The first sound version was shot both in English and in French at Twickenham Studios in 1930, making it the first British bi-lingual production, released in America under the name The Mystery of the Villa Rose. This marked the film debut of Austin Trevor, an actor from Northern Ireland, in the role of Mr. Ricardo. Trevor would go on to be the first actor to create Hercule Poirot on the screen. Veteran British director Walter Summers directed At the Villa Rose, aka House of Mystery in 1940.