After tea at the estate of the Marquis of Gleneyre, a retired British intelligence officer, Anthony Gethryn, is given a list of 11 names by his good friend, Adrian Messenger, and asked to check the whereabouts of the people listed. Subsequently, Messenger is killed in a plane which explodes in midair, and Gethryn learns that all of the other people on the list have also met with seemingly accidental deaths. Knowing that there must be a connection in these deaths, Gethryn enlists the aid of Scotland Yard and receives valuable information from Raoul Le Borg, the sole survivor of the plane crash. Gethryn learns that the killer is a master of disguise who changes his identity for each murder. After weeks of inquiry, Gethryn has concluded that the victims were fellow POW's in Burma and that the killer was the informer who disclosed their escape plans to the enemy. This man is now becoming prominent, and he finds it necessary to remove all those who know of his unsavory past. Gethryn identifies the killer as one of the Gleneyre heirs; in fact, only a small boy is standing in his way of becoming sole owner of the estate. At a fox hunt, the killer, George Brougham, turns up without disguise, but Gethryn decides to let him make his move before arresting him. At the right moment, Gethryn closes in; and the killer dies in one of his own traps while attempting to escape.