A counterspy movement of the Nazis is able to capture a british radio technologist in the occupied Netherlands. Instead of torturing him they treat him well, only asking him to keep on sending messages to England as usual. He decides to fakely cooperate but leaves out his "security check" in his messages; a mistake on purpose that signals his superiors that everything is okay. Despite leaving it out his superiors don't realize he has been caught, instead sending troops and goods as ordered. Soon a german is able to perfectly copy his style, but another captured radio technologist is able to escape to England, dangering this mission.