APRIL: The Mystery of the Spanish Chest
No references. But the name of a song (“Nobody’s Sweetheart”, 1924) is mentioned (and described as “modern”), and Poirot is dancing Charleston (origin: mid-twenties). This setting would also fit with the other cases I have placed in the late Twenties and early Thirties. Poirot either knows someone (having helped them solve a crime earlier, e.g. Lady Chatterton, Prince Paul of Maurania), is introduced to them through Hastings (e.g. Hunter’s Lodge) or takes on seemingly trivial matters (the kidnapping of Johnnie Waverly, the husband poisoning his wife in Cornwall).
SEPTEMBER: The Adventure of Johnnie Waverly
No references. The weather indicates autumn. Poirot is established in Whitehaven Mansions. This episode makes a point of referring to Miss Lemon's project of creating the perfect filing system. It would thus make sense that Poirot has just moved into Whitehaven and recently acquired Miss Lemon's services.