In the middle of the Sahara desert, French Foreign Legionnaires Sgt. Mike Kincaid, Corporal Luis Delgado and Corporal Pierre Molier travel disguised as an Arab merchant and his daughters, in an attempt to discover the whereabouts of a Riffian tribe led by the shrewd Caid Hussin. The men are stopped by a small Riff band, led by Hussin's lieutenant Yassif and when the Arabs grow suspicious, Mike and his men overthrow them and kidnap Yassif. In the city of Tarfa, Legionnaire Lt. Kruger struggles to keep order among the skeleton crew, who have been left at headquarters while Major Bertot and the 42nd Regiment are on maneuvers. When Mike and the men bring in Yussif, Kruger tries unsuccessfully to get him to reveal Hussin's location, but instead discovers Mike's interest in Marie DeLatour, Kruger's girl friend. Kruger goes to Marie's apartment, where he discovers her with Mike, who is arrested after striking Kruger. Delgado and Molier sneak Mike some food in jail, which he shares with Yussif, who is imprisoned in the cell next to him. In gratitude, Yussif advises Mike to escape, as Hussin will attack the nearly empty fort the following day. Mike demands to see Kruger and insists that with a squad of men he can stall the Riff attack for the five crucial days before the regiment's return. Kruger refuses to assign the few men defending the city to Mike and instead offers imprisoned soldiers, guaranteeing the freedom of any man who survives the mission. Delgado and Molier volunteer and the inmates agree to the plan, believing they will escape at the first opportunity. To their disappointment, they soon realize that Mike seriously intends to fulfill the mission. The men soon come across the camp of Sheik Ban Allal, where Mike notices several men in Hussin's tribal robes. Suspecting that the tent these men guard may be an ammunition dump, Mike and three men go undercover and sneak inside, only to find a harem of the sheik's daughter Mahla and her attendants. They are preparing for Mahla's wedding to Hussin, which will unite the two tribes. Sensing that the sheik is unhappy about the pending nuptials, and certain that a postponement of the wedding would interfere with the invasion plans on Tarfa, Mike kidnaps Mahla. She resists and makes several attempts to escape, causing the death of a soldier. That night, while Mike steals horses from a nearby Riff camp, the men, led by the lecherous Jardin, attack Mahla, but Mike returns in time to rescue her. Having followed Mike, the Riffs surround the soldiers and demand Mahla's return. Another soldier dies in the attack, but when a sandstorm hits, the remaining Legionnaires and Mahla escape and search desperately for water. Mahla bribes Jardin to help her escape when they reach an oasis. Nearby, the men discover a wrecked payroll truck filled with money, but Jardin, having been paid by Mahla, cautions the men that the money is traceable. That night, to protect her, Mike binds Mahla to him, and when she realizes Jardin intends to murder Mike, she warns him in time. Jardin breaks away with the payroll money but is shot by Delgado, alerting the Riffs to their location. The next day, Mike and Mahla lead a decoy of horses while the men head off on foot to the city. When the Riffs discover the ruse, they eventually capture the pair, but Mahla forbids Hussin to torture Mike for information about the regiment's return. Mahla demands that Hussin free Mike or she will refuse to marry him, and he complies. As the tribe hastily prepares for the wedding ceremony, Mike's men join them disguised in robes. During the ceremony the men cause a commotion, and Mike and Hussin fight over Mahla, but Ban Allal's tribe turns against Hussin and kills him. Upon returning to Tarfa, Mike and the men are awarded medals by Major Bartot and a resentful Kruger, as Mahla and her father watch in approval.