The head of the cipher bureau, Phillip Waring, is about to marry his secretary, Helen Lane, when he is informed that the state department has discovered a message that must be decoded. With the information given, Waring and his assistant, Lieutenant Murdock, investigate, but their every move seems to be known to their alien adversaries. Helen discovers that Arlie Johnson, interpreter for the bureau, is the real leader of the spy ring, but before she can relay the information she falls into the hands of Johnson and his spy-ring henchmen.