A French professor secretly leads a band of desert freedom fighters.

In Morocco, a band of Riffs successfully attack a caravan of Arabs carrying supplies to the most powerful man in the area, Sheik Yousseff, despite the escort provided by French Legionnaires under Capt. Claud Fontaine. After reclaiming food and supplies that Yousseff's men stole from their villages, the Riffs's leader, El Khobar, orders that they leave behind the Legionnaires' machine guns. However, the Arab Lachmed, who is employed by Yousseff, hides the guns, pretending they were taken by the Riffs, and gives them to Yousseff for later use. At his palace, Yousseff, who is feigning friendship with the French until he can drive them out, plans to dishonor El Khobar by having his men, disguised as Riffs, attack villages. Meanwhile, El Khobar takes leave of a small desert village, promising to return when needed. Margot Birabeau, who has escaped from her Paris school and longs for adventure, shows up at the Legion headquarters in the city of Djiba. When her father, Gen. Birabeau, arrives from Paris to check up on reports of dissidence, he decides that his feisty and love-hungry daughter is better off under his watchful eye and arranges for her to be tutored by shy Paul Bonnard, who is a student of anthropology studying native tribes. Overhearing Fontaine urge Birabeau to arm Yousseff against the Riffs, Bonnard interrupts, saying that the Riffs are only protecting themselves against Yousseff's plundering. Meanwhile, sparks fly between the ambitious Fontaine and Margot, who admires adventurous men, but she notices that her father is swayed by Bonnard's argument. The next day, Bonnard cancels Margot's lessons upon hearing a musical phrase repeatedly played by street musicians. This causes his American roommate, Benjy Kidd, who is a resourceful and often annoying newspaper reporter, to wonder about Bonnard's frequent changes of plan. Later, in a desert village, El Khobar shows up, having been summoned by the village leader Hassan, who is concerned that his neighbor Mindar is stirring up the people against Birabeau. El Khobar tells the people that Birabeau, whom he considers a discerning man, may be their salvation, but Mindar attacks him. Although, Mindar is taken to die in the desert on Hassan's orders, El Khobar later rescues him and sends him to Tunis. El Khobar's generosity is witnessed by a village girl, Azuri, whose passion he does not return. Having taken a job as a dancing girl at Yousseff's palace, Azuri has learned that Birabeau, Margot and Fontaine have been invited there. At the palace, Margot undiplomatically baits Yousseff with information she has learned from Bonnard, so Birabeau sends her to the palace garden. Benjy, who is also at the palace looking for a story, dons the veils of a harem girl and enters their private compartment, where he spies weapons, ammunition and a large army in a nearby room. Azuri helps him to safety through a secret palace entrance before Benjy is caught. Bonnard also shows up, but seeing Margot in the moonlight, changes into his alter ego, El Khobar, and romances her. She flirts with him until the palace is attacked by Yousseff's men dressed as Riffs. Believing Fontaine when he tells her that the Riffs are after her father, Margot reveals that El Khobar is in the garden. After eluding Fontaine, El Khobar abducts Margot and takes her to Hassan's village, where he hopes she will see the truth about Yousseff's duplicity. At first, she is a difficult guest, but after witnessing the arrival of Yousseff's victims, whose village was burned down, she again warms toward El Khobar. After returning to Djiba, Bonnard comforts Birabeau with news of Margot's well-being and convinces him to return with him to talk to the villagers. Meanwhile, Mindar has doubled back and joined Yousseff's men, leading them to Hassan's village. When Bonnard and Birabeau arrive, they find Hassan dying, the village in disarray and Margot kidnapped. Birabeau rides away alone, uncertain of Bonnard's integrity, and meets with Fontaine and his men, who have followed. Benjy has also tracked Bonnard to the village and after discovering his roommate's secret life, dresses as El Khobar and leads the Frenchmen on a chase, which allows Bonnard to leave the village unnoticed. After finding the Riffs, Bonnard, as El Khobar, directs them toward the palace, where Benjy, who has by now joined them, shows them the secret entrance. At the palace, Azuri realizes that Margot is in grave danger and is too heavily guarded to sneak out, so she goes for El Khobar, but runs into Benjy in the secret passageway. In the garden, a fight ensues between the Riffs and Yousseff's men. Spotting Margot with Yousseff, El Khobar rescues her with Benjy and Azuri's help. After arriving with the Legionnaires at the palace, Birabeau arrests Yousseff, whom he now realizes has been terrorizing the villagers with a well-supplied army. After the battle, El Khobar is discovered missing. When Bonnard replies that he is dead, Birabeau, who has deduced Bonnard's double life, reveals nothing. Margot, however, grieves and refuses Bonnard's efforts to console her, until he makes her see that he and El Khobar are "one alone."