A desert-bound member of the French Foreign Legion exposes a betrayer to the Legion. He is then sent on a mission among the Arabs to conclude the signing of a crucial peace treaty.

Legionnaires Henri de Beaujolais, Raoul de Redon, and Dufour overstay their leave in Algiers and are thrown into jail. There Henri earns the title "Beau Sabreur," given him by his uncle, General Beaujolais, when he wins a duel with a traitor, Becque. The general, who has plans for the Sahara, entreats Henri to forsake women for France, sending him first to the desert to learn the customs of the people, then to Zaguig, where he meets American journalist Mary Vanbrugh, whom he snubs, remembering his vow. Becque, hearing that Henri has orders to visit Sheikh El Hammel at a distant oasis to discuss a treaty, and hoping to prevent his departure, attacks Zaguig, but Henri escapes with Mary, her maid, and his aides. Out of distrust for Becque, the sheikh agrees to a treaty with the French, and they resist an attack led by the vengeful Becque. Henri kills Becque in a duel and, having accomplished his task for France, confesses he loves Mary.