While pursuing a suspect over rooftops, John "Scottie" Ferguson (a San Francisco police detective) misjudges a leap and ends up dangling from a gutter, over a hundred feet in the air. A policeman tries to help but ends up falling off the roof. Scottie continues to cling to the gutter with no help in sight.
Apparently help does arrive, however, because in the next scene we find out Scottie has retired from the police force, with a fear of heights that paralyzes him and gives him extreme vertigo. His former fiancée, Midge, tries to help him, but he refuses to follow her suggestions.
An old college buddy of Scottie, Gavin Elster, says his wife, Madeleine, is acting strangely and fears she is suicidal. She has become obsessed with a mad ancestor, Carlotta. Gavin asks Scottie to follow her and make sure nothing happens to her. He agrees.
Madeleine is icy, remote, and absolutely stunning. Her obsession with death attracts Scottie, who is still trying to come to terms with the guilt he feels after the police officer died trying to save him. He falls hopelessly in love with her.
When she throws herself into the bay, Scottie drags her out of the water and brings her to his apartment. Soon afterwards, they become inseparable, visiting many historic sites together. One day they visit the mission at San Juan Batista--the site of Carlotta's death. Madeleine runs away from Scottie and begins to climb the tower that Carlotta committed suicide from. Scottie freezes on the stairs, unable to follow Madeline because of his vertigo. With his knuckles whitened on the staircase railing, he watches Madeleine's form drop to the ground.
With Madeleine lost, Scottie goes insane. No one can help, not even Midge, who finally gives up on him. After his condition improves slightly, he starts visiting the same sites that he and Madeleine visited--hoping beyond any rational hope that he will see her again. And eventually he sees a shop clerk named Judy Barton with an uncanny resemblance to Madeleine. Compared to Madeleine, however, the clerk is common, dressing in ordinary, rather cheap clothing and using lots of lipstick and eyeliner.
He begins to court her. He buys her clothes like Madeleine wore and urges her to dye her hair blonde like Madeleine's. They start visiting historic sites around town together, just as he did with Madeleine.
Scottie feels he has restored his true love, that he has re-animated Madeleine. However, it's not quite that simple.
That's all I'm giving away. For more info, see the movie!