Jack Powell (Charles "Buddy" Rogers) and David Armstrong (Richard Arlen) are rivals in the same small American town, both vying for the attentions of pretty Sylvia Lewis (Jobyna Ralston). Jack fails to realize that "the girl next door", Mary Preston (Clara Bow), is desperatly in love with him. The two young men both enlist to become combat pilots in the Air Service. When they leave for training camp, Jack mistakenly believes Sylvia prefers him; she is too kindhearted to disillusion him, but lets David know that she loves him.
Jack and David are billeted together. Their tent mate is Cadet White (Gary Cooper), but their acquaintance is all too brief; White is killed in an air crash the same day. Undaunted, the two men endure a rigorous training period, where they go from being enemies to best friends. Upon graduating, they are shipped off to France to fight the Germans.
Mary joins the war effort by becoming an ambulance driver. When she is in Paris, she learns that Jack is on leave there. She finds him, but he is too drunk to recognize her. She puts him to bed, but when two Military Police barge in while she is innocently changing out of a borrowed dress back into her uniform in the same room, she is forced to resign and return to America.
The climax of the story comes with the epic Battle of Saint-Mihiel. David is shot down and presumed dead. However, he survives the crash landing, steals a German biplane, and heads for the Allied lines. By a tragic stroke of bad luck, he is spotted by Jack, who is bent on avenging his friend. Jack shoots David down. When Jack lands to pick up a souvenir, he becomes distraught when he learns what he has done, but before David dies, he forgives his comrade.
With the end of the war, Jack returns home to a hero's welcome. When he returns David's effects to his grieving parents, David's mother blames the war, not Jack, for her son's death. Then, Jack is reunited with Mary and realizes he loves her.