In the year 1774, a hundred-year-old bridge leading to the chapel of San Luis Rey in Peru plunges into the chasm it spans, killing the five people who are crossing it. Brother Juniper Donald Woods is one of the chapel monks, whose faith is shaken by this tragic event. He travels to Lima to seek answers about why these particular souls were chosen to die in such a brutal way.
In Lima, Brother Juniper [Donald Woods] talks to a well-known local theatre figure called Uncle Pio [Akim Tamiroff], and asks him about a famous actress, Micaela Villegas [Lynn Bari]. Pio then begins recounting the story of his encounter with Micaela and the chain of events that led up to the fateful accident.
Years earlier, when Micaela was rising in Lima's theater world, she was in love with the bold and radiant Manuel [Francis Lederer]. His twin brother, Esteban, loathed her. When Manuel left for Spain, Pio became Micaela's mentor and helped her master her craft, shaping her into a celebrated actress for the Comedia Theater.
Her growing fame and beauty drew the attention of the viceroy, Don Andre [Louis Calhern], who invited her to a private visit at his mansion. Just before Micaela is to go to the viceroy, Manuel returns from his travels, and instead of going to the viceroy, she spends the night with her beloved Manuel.
Tension rises between the twin brothers when Manuel discovers all the letters Micaela has written to him that Esteban neglected to forward. Esteban apologizes and feels guilt over his actions, to the point that he contemplates taking his own life, but Manuel stops him from hanging himself.
After Esteban recovers, Manuel sets off on another long journey. When Micaela is once again invited to the viceroy, she accepts the invitation. Because of the viceroy's interest in Micaela, the Marquesa Dona Maria [Alla Nazimova] feels threatened and decides to eradicate her. The Marquesa pretends to be Micaela's friend to win her confidence, unlike the other prominent guests at the viceroy's table. This is the end of Uncle Pio's tale.
Juniper visits the Abbess [Blanche Yurka], who tells him about the Marquesa and the loneliness that leads her to seek companionship. The Abbess explains that the Marquesa's daughter eloped to Spain and married a young aristocrat, a development that deepens the Marquesa's bitterness. Pio, consulted by the Marquesa about the viceroy and Micaela, appears to have no new information to offer.
The viceroy falls in love with Micaela, and Esteban warns her that the noblemen are scheming to remove her from the scene. Micaela grows distressed and turns to Pio for help, who then gives her a song to perform at the castle. The lyrics hint at a plot to seize the throne, causing the aristocratic audience to react with offense. The viceroy forces Micaela to apologize, but the Marquesa recognizes her own folly and apologizes to Micaela in turn. This moment provokes thoughts on human nature and the possibility of transformation—something both Esteban and the Marquesa begin to glimpse.
Manuel returns from his travels as a captain and asks Micaela to accompany him. The viceroy enters as they embrace and demands to see Manuel at his palace. Manuel is arrested that night, seen by the viceroy as too strong a rival for Micaela.
When the viceroy must return to Spain, he still hopes Micaela will accompany him. She refuses because of Manuel's imprisonment and pleads with Uncle Pio for help in freeing him, before leaving on a mountain trip with the viceroy and his entourage.
Pio succeeds in securing Manuel's release, though he is later interrogated by the viceroy. Pio counsels the viceroy not to kill Manuel, arguing that a martyr would only strengthen him. Following this advice, Manuel is pardoned, and Pio brings the signed document to the location where Manuel is hiding near the bridge to San Luis Rey.
Soon after, the viceroy and his small party—Micaela, the Marquesa, Pepita, and their scribe Esteban—arrive at the bridge. The viceroy crosses first, followed by the others. Just as Micaela is about to step onto the bridge, Manuel appears, stops her with a kiss, and she takes only one step before the bridge collapses. The viceroy, the Marquesa, Esteban, Pepita, and another man fall to their deaths, while Micaela is saved by Manuel.