Based on a novel by Robert Hichens, a Trappist monk renounces his vows and marries a beautiful woman in North Africa but is called back to God in the desert.
Lonely Domini (Marlene Dietrich) returns to her convent after caring for her dying father and is told to go to the desert. At a Trappist monastery in North Africa monks take vows of poverty, chastity, and silence. Visiting soldier De Trevignac (Alan Marshal) learns that brother Antoine has fled. On a train Domini sees Boris Androvsky (Charles Boyer). The poetic Batouch (Joseph Schildkraut) serves her, and Father Roubier (C. Aubrey Smith) welcomes her. Batouch takes Domini to see dancers. Boris is entranced. When the dancer tries to stab Hadj (Henry Brandon), Boris helps Domini escape and walks her home. They go riding and at an oasis meet Count Anteoni (Basil Rathbone). Women find the cross Boris is wearing, and he throws it in the water. Anteoni says it is unwise not to acknowledge one's God in the desert, the garden of Allah. A sand diviner (John Carradine) tells Domini she will find joy in the desert but warns her. She asks Boris why he is troubled; but he says she has made him happy. Boris tells Father Roubier he has no use for his church. Domini tells Father Roubier she thinks Boris has lost his faith, and the priest warns her too. Boris tells Domini he is going but then says he loves her. They are wed by Father Roubier in his church. Count Anteoni wishes them well, and they go on a caravan into the Sahara.
Boris tells Domini to think only of him. She prays for her love to be tested so he will know. One night while Domini is waiting for Boris on a tower with a torch, De Trevignac sees it, saving his lost platoon. At dinner De Trevignac remembers Boris and leaves suddenly without telling Domini why. Boris won't tell her his trouble. Count Anteoni finds Domini after seeing De Trevignac and asks for the monastery's liqueur, saying a monk left with the liqueur's secret. Domini disapproves, but Boris defends his right to love and happiness. Anteoni tells Domini it is true and leaves. Domini asks Boris why he broke his vows. Boris says he had a lonely happiness but then was allowed to talk with visitors and saw romantic love. He fled and met her. She says no one is bad who loves. Boris decides to go back to make reparation. He and Dominic say good-bye to Father Roubier and Batouch. She tells Boris they will be together in the next world. He goes into the monastery, and she cries.
This early color film has a mystic mood pervading the conflict between religious and romantic love, which is relieved only by the comedy of Batouch. Although gibberish is spoken instead of Arabic, the two religions are not in conflict in this mystical story.