On May 10, 1941, Rudolf Hess, Deputy Führer of Nazi Germany, flies to Scotland on his own initiative to negotiate a peace treaty between Britain and Germany.

Furious, Adolf Hitler orders his secret agents in Britain to locate Hess and kill him. MI5, the British secret service, intercepts the message and uses it to smoke out German agents in Britain, employing two Hess look-alikes as bait.  

German Military Intelligence sends an SS assassin, Major Helmut Kirchgässner, to Britain to kill Hess.  

A tense game of cat-and-mouse ensues in southeast England and western Scotland, with multiple cats and multiple mice.