A mail flyer joins the Canadian air force for fun but has to prove his worth when he goes to war.

For several years, bush pilots Johnny Dutton, Tiny Murphy, Blimp Lebec and Scrounger Harris have shared the work in their area of Canada. To their dismay, they now find that they are often beaten to the jobs by a new flier, Brian MacLean. Determined to get their revenge, Johnny, Tiny, Blimp and Scrounger chase Brian's airplane and force him to land near the store owned by Foster and his gold-digging daughter Emily, who is also Johnny's fiancée. While leaving his plane, Brian slips and injures his head. When Johnny sees how bad the injury is, he flies to the nearest town to fetch a doctor. By the time Johnny returns, the lake is fogged in, so the other pilots light bonfires to guide him. Johnny lands safely with the doctor, who performs an emergency operation. Although Emily begs Johnny to take her with him when he leaves, Johnny is determined to earn enough money to start his own airline before they get married. Brian stays behind to recuperate, and during his convalescence, he and Emily grow attached to each other. When Johnny returns, he invites Brian to join him and Tiny in a job flying explosives to a mine. Brian agrees after he learns of the heroic effort Johnny made to save his life and breaks off his relationship with Emily for the same reason. The three pilots make enough money for Johnny to start an airline with his share. Brian warns Johnny that if he marries the gold-digging Emily he will not have the money for long, and Johnny angrily strikes out at him. Brian knocks Johnny unconscious in the fight and, determined to prevent his friend from making a serious mistake, marries Emily himself. Johnny follows them to Ottawa, but when he learns that they are married, he gives his pay to charity and joins the Royal Canadian Air Force. Now that he knows Johnny is safe from Emily, Brian gives her his pay and leaves her for good. Back in the woods, the other pilots, inspired by a speech by Winston Churchill, join the air force too, but are disappointed to learn that they are too old to fly fighter planes. Their experience makes them valuable teachers, however. Brian has trouble adjusting to military discipline and, after he crashes a plane, is dismissed from the service. Then, during a military ceremony, Brian buzzes the field and causes Tiny's death. When an urgent call goes out to all pilots to help fly planes to England, Brian volunteers using Tiny's name as a pseudonym. Just outside of England, the pilots encounter a German Messerschmidt, whose pilot shoots at the defenseless planes. When Scrounger, who is acting as Brian's navigator, is killed, Brian defies orders once again and crashes his plane into the German, killing them both. Thanks to his efforts, the rest of the squadron files safely into England.