John Martin is part of an American spy team dropped into France during World War II to destroy the French railway system. After successfully blowing up a tunnel he runs back to save Ellen and is told "Never come back for me again." Later he must choose whether or not to obey her wishes.
During World War II, Allies are aided by O.S.S. agents (Alan Ladd and Geraldine Fitzgerald) who are sent to France to destroy the Corbett Mallon railroad tunnel that German invaders are using to ship supplies to the troops. They succeed in their mission and fall in love in the process. But, commitment to duty interferes with their love for each other.