At the time of World War II, Serge enlists in the U.S. Marine Corps and learns the rudiments of military undercover work. By the late thirties, he's an aeronautical engineer and ready for the real thing military-industrial espionage at the highest level, in Nazi Germany.
At first the darling of the German High Command, Serge runs afoul of the Gestapo and is forced into perilous escape. But then he has to go back, back into occupied Europe, because the woman he loves is trapped in a ghetto in Belgium and he cannot let her die.