During World War II, talented leader Sgt. Kelly (Thomas Mitchell) takes under his wing a reserved and somewhat insecure junior officer, Cpl. Colin Spence (Henry Fonda), while leading a regiment of soldiers through the Libyan desert. A reluctant pupil, Spence is preoccupied with daydreams of his home-front girlfriend, Valentine Lee (Maureen O'Hara). But when a plane crash seriously wounds Kelly and cripples their means of navigation, Spence is forced to take command of his fellow soldiers.