After a rooftop chase in which a fellow policeman falls to his death, San Francisco detective John "Scottie" Ferguson retires due to acrophobia and vertigo caused by the incident. Midge, his ex-fiancée, says that another severe emotional shock may be the only cure. Midge retains feelings for Scottie, but he is not receptive to her intimations.
Gavin Elster, an acquaintance from college, asks Scottie to follow his wife, Madeleine, claiming that she has been behaving strangely. Scottie follows Madeleine to the grave of Carlotta Valdes (1831–1857) at the Mission San Francisco de Asís and the Legion of Honor art museum, where she gazes at the Portrait of Carlotta.
A local historian explains that Carlotta Valdes committed suicide: she had been the mistress of a wealthy married man and borne his child, and the otherwise childless man kept the child and cast Carlotta aside. Carlotta, who Gavin fears is possessing Madeleine, was Madeleine's great-grandmother. However, Madeleine does not know this or remember the places she visited while ostensibly possessed. Scottie trails her to Fort Point and rescues her after she jumps into San Francisco Bay.
The next day, Madeleine stops to deliver a letter of gratitude to Scottie, and they spend the day together. They travel to Muir Woods and Cypress Point on 17-Mile Drive, where they embrace. The next day, Madeleine recounts a nightmare, and Scottie identifies its setting as Mission San Juan Bautista, Carlotta's childhood home. He drives her there, and they express their love for each other. Madeleine suddenly runs into the church and up the bell tower. Scottie, halted on the steps by his fear of heights, sees Madeleine plunge to her death.
An inquest into Madeleine's death declares it a suicide, though the coroner rebukes Scottie for not doing more to save her. Gavin also does not fault Scottie, but Scottie becomes clinically depressed and is sent to a sanatorium in an almost catatonic state. Following his release, he frequents the places that Madeleine visited, often imagining that he sees her. One day, he notices a woman on the street who, although superficially very different, reminds him of Madeleine. She identifies herself as Judy Barton, from Salina, Kansas.
A flashback reveals that Judy was the person Scottie knew as "Madeleine Elster." She was impersonating Gavin's wife in an elaborate murder scheme; Gavin took advantage of Scottie's fear of heights to substitute his wife's freshly killed body in the apparent "suicide jump." Judy considers confessing her involvement in the plot to Scottie but continues the charade because she loves him.
They begin seeing each other, but Scottie remains obsessed with "Madeleine" and asks Judy to change her clothes and dye her hair to resemble her. After she complies, he notices her wearing the necklace portrayed in Carlotta's painting. He realizes the truth and drives Judy back to the Mission.
There, he tells her he must re-enact the event that led to his madness. He tells her that he now knows that "Madeleine" and Judy are the same person, and Judy was Gavin's mistress before being cast aside just as Carlotta had been. He forces her up the bell tower and makes her admit her deceit. He reaches the top and conquers his fear of heights. Judy confesses that Gavin paid her to impersonate a "possessed" Madeleine and begs Scottie to forgive her. He embraces Judy, but a shadowy figure — a nun investigating the noise — rises from the tower's trapdoor, startling her. Judy lunges backward and falls to her death. Scottie, bereaved once again but cured of his fear of heights, stands on the ledge in shock while the nun rings the mission bell.
