In chapter 25, Hastings tells Donald Ross that Poirot has left for an appointment relating to his investigation of another case, "the strange disappearance of an Ambassador's boots". When Poirot returns from the appointment, he tells Hastings that it was a case of cocaine smuggling, and that he had spent the last hour in a ladies' beauty parlor. This case sounds identical to the one in the Tommy and Tuppence story, "The Ambassador's Boots" from "Partners in Crime" (1929), except that Poirot mentions a girl with red hair (Hastings is often described by Poirot as partial to redheads), while the girl in "The Ambassador's Boots" has blonde hair, or black hair when in disguise.