A close-knit band of inventive boys build and fly lightweight aircraft, confronting engine troubles, rivalry, and thieves as they prepare for a major air voyage and competitive race. The episodic plot follows tests, midnight alarms, a dramatic message from above, discoveries that complicate their plans, and a daring ascent toward a mountain summit during the climactic aerial contest. Practical problem-solving, resourcefulness, and camaraderie drive the action, culminating in the exposure of wrongdoers and a hard-won victory in the race.