Captain Harvey

In the short story The Crag in the Dolomites, (later chapter 17 and 18 of The Big Four), Captain Harvey is a British intelligence agent who works with Hercule Poirot in planning the destruction of the crime syndicate known as "The Big Four".

While Poirot remained hidden in the town of Spa in the Ardennes planning the strategy, Harvey acted as his go-between, passing his instructions and messages to the governments involved. He kept Poirot informed of developments, especially the movements of the members of the Big Four. When Abe Ryland arrived in Europe, and Madame Olivier had left Paris for Lago di Carezza in Italy, Harvey surmised that the Big Four was gathering at their headquarters and told Poirot that the time had come for him to move. He accompanied Poirot and Hastings on their way to their final confrontation with the Big Four.

Poirot considered Harvey to be one of the most efficient members of the British Intelligence Service, although Harvey himself was careful to keep under cover. Most of his friends and acquaintances thought he was an amiable but brainless young man who was devoted to the foxtrot dance.