In Kurdistan during World War I, Michael Andrews (Cary Grant) is a British officer captured by Kurds, imprisoned, and awaiting execution. The local Turkish commander (Claude Rains) helps Andrews escape and confides that he is a British intelligence officer (initially “Smith,” later named as John Stevenson) in disguise. The two set out to warn friendly villagers of a pending Kurdish attack. After a difficult river crossing, and after Andrews flirts with a married tribal woman, Stevenson returns to espionage. Andrews, who has hurt his leg, goes to Cairo for medical treatment. There, Andrews falls in love with his nurse, Rosemary Haydon (Gertrude Michael), who ultimately refuses Andrews by saying she’s secretly married to an unnamed man she’d known briefly a few years before.
Andrews transfers to the Sudan, where his patrol takes over a fort after finding that its troops had been massacred. Meanwhile Stevenson goes back to Haydon—revealed as his wife—who confesses her love for Andrews. Stevenson requests a transfer to the Sudan to confront Andrews. Shortly after Stevenson reaches the fort, thousands of African tribesman attack it. Realizing that a handful of men can’t hold the fort, Andrews, Stevenson, and their troops set out over sand dunes and eventually enter the jungle with the tribesmen in hot pursuit. British troops appear out of nowhere, deus ex machina, defeat the tribesmen, and rescue Andrews. Stevenson, mortally wounded in the battle, dies a hero’s death, presumably leaving Andrews free to marry widow Haydon.