A member of the French Foreign Legion falls for an Arab woman whose family has sworn to kill all foreigners.

In 1939, Jala, the brother of the Dylak sheik in French Morocco, arranges to assassinate his sibling, whom he considers a weakling. The assassins are dressed as French Legionnaires, and the sheik's young children, El Zanal and Princess Zara, witness the killing and vow never to forgive the foreigners. Fifteen years later, the soldiers at Ft. Valeau in the Sahara Desert eagerly await the relief column that is marching toward them. Jala, disguised as a wine merchant, arrives at the fort and questions Sgt. Diepel about a rumor that no radio reports have been received from the relief troops. The men are surprised when the new commander, Capt. David Malcolm, arrives ahead of his troops in a helicopter, but Malcolm explains to Capt. Montclair that he received his orders too late to join the march. Montclair warns Malcolm that there has been no radio contact with his troops, but Malcolm is not worried, as the neighboring Dylak tribes have been peaceful for years, and Montclair turns over his command and departs in the helicopter. After Montclair's departure, Malcolm interviews Pvt. Pete Havers, an alcoholic but charming Englishman, and sends him to the guardhouse for being drunk while on duty. That night, a sentry spots a burning cross in front of the fort, and the men are horrifed to discover the mutilated bodies of eight men from the relief column. Malcolm orders Dr. Kleiner to revive his friend, Lt. Rene, despite the great pain it will cause him, and before dying, Rene whispers that El Zanal, the current Dylak sheik, was responsible for the massacre. The next day, the men, especially the cowardly Ducco, bemoan their situation, but Malcolm is encouraged by a radio report that Maj. Henri Panton is marching with a full battalion to aid them. While Malcolm is wondering what drove El Zanal to commit such an atrocity, a large group of Arabs appear before the fort. When three of the men wave a flag of truce, they are taken to Malcolm's office, and there the spokesmen order Malcolm to surrender. Knowing how well-provisioned the fort is, Malcolm dismisses the mens's threats, but as they leave, they blow up the fort's gates. During the ensuing battle, wave after wave of Arabs descend upon the fort, until finally, the legionnaires are forced to surrender. The remaining soldiers are confined to the barracks, and there El Zanal tells Malcolm that he knows about Panton's imminent arrival and intends to rebuild the fort and ambush the unsuspecting battalion members when they enter. El Zanal informs Malcolm that he has gathered intelligence on the fort's men and knows which ones will cooperate with him to save their lives, then offers safe passage to Malcolm and the others if they will also assist in luring Panton. Knowing that the traitors will help anyway, and that the only way he can save the battalion is to stay alive, Malcolm accepts El Zanal's offer, much to the astonishment of his men. Hot-headed Texan Rex Tyle hits Malcolm, but after the captain explains his reasoning, the chagrined soldiers vow to stand beside him. Malcolm also informs his men that there are explosives hidden in the vault below his office, with which they can warn the approaching column, even though it will mean blowing up the fort and everyone in it. Meanwhile, Zara, who always rides at her brother's side, has become intrigued by Malcolm and sends for the handsome American. Zara reveals that legionnaires assassinated her father, and becomes enraged when Malcolm protests that soldiers would never commit such an act. The next morning, the tribesmen begin rebuilding the fort, and El Zanal receives a radio report that Panton will arrive the following day. While discussing Malcolm with El Zanal, Zara learns that her brother intends to kill all of the fort's legionnaires, regardless of their actions. El Zanal warns Zara that no foreigner could ever understand their way of life, but nevertheless, Zara attempts to persuade Malcolm to join them. Malcolm kisses the princess but rejects her offer, then rejoins his men. While Malcolm plots with the soldiers, Zara informs her brother that she has fallen in love with the captain, and he promises to allow Malcolm to live if he proves trustworthy during the coming battle. Malcolm meets with Zara again, and to her chagrin, ties and gags her before stealing her bodyguard's robes. Several other soldiers join him in the vault to get the explosives, but they are caught by El Zanal, who reprimands his sister for believing that Malcolm loved her. The next day, Ducco and several other traitors, along with the Dylaks, stand guard on the fort walls, while the rest of the soldiers are locked in a barn with the horses. Malcolm is tied to a post in his office, so that he can watch the slaughter of the battalion, while in another room, El Zanal reveals to Jala that he knows the true identity of his father's murderers. Afraid that he is going to be killed, Jala tries to explain himself and is astounded when El Zanal thanks him for his act and for teaching him to rule without sentiment. Zara, who overhears the exchange, is infuriated and swears that she will never stand beside her brother again. While the tribesmen prepare for the arrival of the battation, Zara and her maid, Alita, kill Jala and rush to free Malcolm. The fort gates open and Panton's men advance as Malcolm frees his men and finds weapons. A huge gun battle ensues, during which Havers is killed and Malcolm shoots El Zanal. Later, with peace restored, the remaining Dylaks are rounded up, and Panton assures Malcolm that Zara's efforts to help him will earn her a lenient sentence. Malcolm smiles at Zara as she joins her people, then watches proudly as the French flag is raised.