Captain Kent

In the short story The Lady on the Stairs (later, chapters 5 and 6 of The Big Four), Captain Kent was an officer of the U.S. Secret Service. He came to London to call on John Halliday but found that he had disappeared. Kent then called on Chief Inspector Japp who introduced him to Poirot and Hastings. According to Kent, the U.S. authorities had captured documents which mentioned the Big Four. These documents described a weapon capable of focussing a powerful beam of wireless energy on a given spot.

Kent was described as a tall, lean American, with a "singularly impassive face which looked as though it had been carved out of wood."