While visiting the estate of the Marquis of Gleneyre, retired MI-5 officer Anthony Gethryn is asked by old friend Adrian Messenger to look into the backgrounds of the ten people on a list he has made. He's somewhat secretive about what it is he wants to learn but Gethryn agrees. When Messenger is killed while en route to Montreal - a bomb explodes and destroys the aircraft in mid-flight - Gethryn comes to believe that Adrian's list should have perhaps had an eleventh name on it - that of Adrian Messenger. Most of those people have died, usually in the form of some accident or another and he is now convinced that they were all murdered. Working with a survivor from the airplane disaster, Max Karoudjian - himself a former fighter in the French Resistance during the war - Gleneyre tries to determine who would want to have them all killed.