The narrative opens in the fall of 1918 during the final, desperate American push through the heavily fortified Argonne Forest. Aviators Tom Raymond and Jack Parmly wait anxiously for the signal to launch their battleplanes, eager to use their new American-built aircraft powered by Liberty motors. Once aloft, they encounter fierce opposition from German air patrols and face deadly hazards from hidden machine-gun nests below. During a dogfight, Tom's engine fails, sending him plunging dangerously close to enemy lines before he manages a miraculous recovery.
While grounded temporarily, Jack unexpectedly encounters a small French orphan named Jeanne, who carries a tattered letter written by her dying mother. The note reveals that Jeanne's twin sister, Helene, was abducted by their treacherous half-brother, a German general named Anton von Berthold, who hopes to seize their valuable estate in Lorraine. Moved by the tragedy, the two chums vow to rescue Helene whenever an opportunity arises, cementing their determination to outwit the villainous general.
As the American offensive intensifies, Tom and Jack continue their dangerous scouting missions, helping to direct artillery fire onto heavily fortified German positions known as strongholds. They participate in a massive nighttime bombing raid that targets high-level enemy headquarters, braving anti-aircraft fire and hostile aircraft to deliver critical blows. Despite the chaos of war, the pilots display remarkable courage and tactical skill, earning the deep respect of their comrades and commanding officers.
Using a brief leave and a clever ruse to secure essential fuel from German military cars, the chums execute a daring clandestine mission behind enemy lines to reach General von Berthold's chateau. Navigating the ancient building under the cover of darkness, they locate and liberate little Helene, executing a daring escape under heavy pursuit. The narrative culminates in the triumphant breakthrough of the Argonne lines, leaving the air service boys ready for their next chapter of service as peace finally looms on the horizon.
