Three young aviators race across wartime Europe in their airship to free a captured friend accused of espionage. Their journey moves from uneasy cities to forests and besieged strongholds, and includes reconnaissance flights, clashes with enemy airships and ground forces, narrow escapes, a prison rescue, and attempts to uncover conspirators. Encounters with hostile troops, harsh landscapes, and mechanical peril test their skill and loyalty, leading to a climactic aerial battle, the tragic loss of their vessel, and revelations that explain how their comrade came to be detained.