After a German
U-boat drops off Nazi saboteurs, RCMP Corporal Wagner (Flynn) captures the leader, Colonel Hugo von Keller (
Helmut Dantine), the only survivor after an avalanche wipes out the rest of the group. Wagner persuades his colleague to go to report and allow von Keller to recover. Von Keller discovers that Wagner speaks German and is of German ancestry, and probes his views on the war. Wagner appears potentially sympathetic to the German cause. However, the RCMP suspect Wagner of disloyalty and despatch a patrol to bring both men in. Wagner, seemingly under suspicion by the RCMP of being a Nazi sympathizer, asks successfully to be discharged from the force. After being sent to a prisoner of war camp, von Keller leads an escape of other German soldiers. Wagner is subsequently contacted by Ernst Willis (
Gene Lockhart), an enemy agent, who hires him as a wilderness guide. Wagner and his new confederate set out for the north by train, while a pursuing Mountie who makes contact with Wagner is killed by the agent. Wagner is taken to von Keller and convinces him that he is loyal to Germany and can guide him and his companions through the Canadian wilderness to a mysterious destination. His fiancée Laura McBain (
Julie Bishop) is held as a hostage to ensure his loyalty but Wagner, acting as a double agent, manages to send a message to police headquarters to alert them of the Nazi saboteurs' plans. Fellow Mountie Jim Austin (
John Ridgely) follows their trail, but is spotted and killed, along with Willis and a native Canadian porter, before the group reaches a mine shaft where bomber components have been secreted before the war. The bomber is assembled and takes off for its mission: to bomb the main waterway between the United States and Canada to disrupt transatlantic shipping of war materials. Wagner manages to escape, climbs aboard the aircraft to shoot the crew, and parachutes to safety before the bomber crashes. After recovering from a wound he received during the skirmish on board the aircraft, he and Laura marry. ==Cast==