In Agatha Christie’s short story, “The Adventure of the Cheap Flat,” Poirot’s suspicions are aroused when he hears of a sweetheart deal on a flat. Doing a little freelance investigating, he soon learns that the flat is at the center of a case of international espionage and a potentially fatal double-cross. This short story originally appeared in the May 9, 1923 issue of The Sketch magazine.