A German submarine surfaces somewhere in the frosty wasteland of Northern Canada (Hudson Bay?). The submarine disgorges a party of Germans led by a Luftwaffe officer, Col. Hugo von Keller. Hugo, the other Germans, and their Inuit guides set off to destination unknown—until an avalanche in a mountain pass kills everyone in the party except for Keller.
Keller staggers across the snowy plains of the Canadian north for a while until he collapses. Fortunately for him, he's picked up by a couple of Canadian Mounties, Steve (Errol Flynn) and Jim. Steve, who is the son of German immigrants, is rather excessively solicitous for Hugo's welfare, which makes Jim vaguely suspicious. When a second group of Mounties is dispatched to bring both Hugo and Steve in, Steve is so offended that he quits the service on the spot.
Later, when Hugo escapes from a POW camp, Steve is arrested as a precautionary measure. He is so angry that he says in public that "Canada can go to the devil." A bitter, angry Steve is receptive when von Keller's American handler, Ernst Willis, approaches him and asks for help with von Keller's mission. What von Keller and Willis don't know is that Steve's disaffection with Canada and new sympathy for the Nazis is all a ruse, and he is actually working to infiltrate their group and thwart von Keller's mysterious mission.
- Cannot Keep a Secret: Steve's girlfriend Laura gets Jim to tell her that they captured a German spy. He swears her to secrecy. Less than five minutes later she's telling her father.
- Cassandra Truth: The local guides urge von Keller to avoid the mountain pass and take the longer but safer route around. Keller refuses, and everyone in the party but him are killed by an avalanche on the mountain pass.
- Chekhov's Skill: Von Keller enters Canada in uniform so he won't be shot as a spy—and he wears a Luftwaffe uniform. It turns out the secret mission is to assemble a hidden plane and bomb "the main waterway between the United States and Canada" (the Erie Canal, maybe?).
- Gasoline Lasts Forever: The disassembled plane was hidden in the Canadian far north sometime before the start of the war. In 1943, after they put it together it starts right up.
- I Lied: Steve breaks his cover to warn Jim when Jim approaches their party. As von Keller's mooks are about to shoot an unaware Jim, Steve begs them not to and promises to get Jim to surrender. Steve approaches Jim and gets him to put down his rifle—and von Keller has Jim shot.
- The Infiltration: Steve and the Mounties are running a scheme in which Steve pretends to change his allegiance to Germany in order to infiltrate Von Keller's group. It only partially works, as a suspicious von Keller has Laura brought along on their trip as a hostage.
- Spiritual Predecessor: This film can considered to be Cliffhanger except set in WWII Canada with the Nazis being the invaders rather than Treasury robbers, as they have a premise about a small Dwindling Party of terrorists stranded on a snowy mountainous terrain (which gets a dose of Scenery Porn) and trying to escape with the aid of their hostage, while the audience would cheer for The Hero to put a stop to them.
- Spy Fiction: A German mission to drop some commandos in Canada, where said commandos will retrieve a long-hidden plane and bomb a crucial waterway.
- Spy Speak: The Trust Password variant. German agents recognize each other this way: the first agent says "Cold country, Canada," and the second says "You think this is cold, you ought to go up north where I'm going."
- Surprisingly Good English: Ernst and Steve look around the rustic Inuit cabin where they have stopped. An unimpressed, obnoxious Ernst says "These people live like swine." Their guide's Inuit wife, previously heard only to speak in her native language, says "Maybe you live worse if things be the same for you."
- Third-Person Person: Laura's goofy father Angus McBain has a habit of lapsing into this."McBain will put up no bail for a man who would damn his own country."
- Throwing Your Gun at the Enemy: Subverted. Steve throws his gun after he runs out of ammo—but at the light in the tunnel, to knock it out.
- Turn in Your Badge: Steve is fired from the Mounties for pro-German leanings. In actuality it's a ruse to infiltrate the German spy ring.
- You Have Outlived Your Usefulness: Von Keller demands that Willis, an older and not terribly fit man, accompany them on the trek to the plane. When Willis can't keep up, von Keller shoots him. Willis even says "I'm not useless!" right before von Keller pulls the trigger.