Sydney Crowther

In the short story The Terrible Catastrophe, (later chapter 15 of The Big Four), The Right Honourable Sydney Crowther was the Secretary of State for Home Affairs. He was some fifty years of age and a well-known and popular political figure. Hastings noted that Crowther received Poirot and him with "that delightful bonhomie of manner which was well known to be one of his principal assets."

In the days following the killing of Flossie Monro, Poirot laid out before Mr Crowther and Monsieur Desjardeaux, the French Prime Minister, all that he knew about the Big Four. Poirot considered that since he had unmasked the identity of Number 4, his own life was at risk. Crowther was inclined to believe Poirot. He told the more sceptical French premier that Scotland Yard had been forced to admit that Poirot was right in many of his claims. The only question was the extent of the objectives of the Big Four.

Poirot left Crowther a key to a safe deposit box in which he had placed all his notes about the Big Four. Crowther said that Poirot had converted him, fantastic as the account may seem.