We see Detective John "Scottie" Ferguson climbing up onto a roof as he and a policeman chase a criminal. Suddenly, Scottie nearly falls from a ledge, and looks down at the ground beneath him. The policeman tries to climb down to help him and holds out his hand, but Scottie is frozen in fear. When Scottie is unable to reach up, the policeman falls to his death.
The scene shifts to later. Scottie and Midge, his ex-fiancée and close friend, sit in her apartment. She does some sketches, while Scottie sits in the chair, evidently healing from injuries endured in the chase. He tells Midge that they're taking his corset off the next day, asking, "Midge, do you suppose many men wear corsets?" to which she replies, "More than you'd think."
Midge asks Scottie if he's going back to work, and references the fact that he used to be a "bright young lawyer" who decided he wanted to be a detective. He tells her he had to quit because of his fear of heights, and suggests that he feels responsible for the policeman's death. Midge reassures him that it's not his fault, and tries to discourage him from quitting, suggesting that he ought to take a desk job.
Suddenly, Scottie notices a brassiere that Midge has hung up for her fashion drawings. She tells him it's a brassiere without shoulder or back straps, and that an aircraft engineer designed it. He asks Midge if she's going to get married, and she tells him that he's the only man for her, even though they were only engaged for three weeks. Scottie accuses Midge of calling off the engagement, then asks her if she remembers a "Gavin Elster" from college. He tells her he got a call from Gavin, and the number seems to be from a rough part of town.
Before he goes, Scottie asks Midge if she wants to go for a drink, but she tells him she has to work. As he walks out, Midge tells Scottie that her doctor told her the only way for Scottie to get over his fear of heights is to go through another emotional shock. Scottie suggests that if he can get used to heights a little bit at a time, he can conquer his traumatic memory. To demonstrate, he stands on a stool to show his theory. When Midge puts a higher stool out, he goes higher, but suddenly catches a glimpse of the height out the window, and falls down, terrified.
The scene shifts and we see Scottie visiting Gavin Elster, who is running some sort of shipbuilding business near a bustling construction site. Gavin tells him he's been back for almost a year, and that he heard that Scottie has quit the force. "What's on your mind, Gavin?" Scottie asks, and Gavin asks Scottie to follow his wife because he is worried she is going to be possessed by a ghost from the past. "Scottie, do you believe that someone from the past, someone dead, can enter and take possession of a living being?...If I told you that I believe this has happened to my wife, what would you say?" Gavin says.
When Scottie expresses his skepticism, Gavin decides that he is not the man for the job, then details the ways he believes his wife is somehow possessed by spirits from the past. "A cloud comes into her eyes and they go blank," he says, discussing the fact that his wife seems to be under some kind of metaphysical spell, and that it is happening more and more. He also tells Scottie that she has started wandering, and that he recently followed her to Golden Gate Park, but had to go back to work and could not continue to monitor her, but when he checked the speedometer on her car later, it said she had driven 94 miles. Scottie doesn't want to do it, but Gavin tells him they're dining at Ernie's and then going to the opera that night, and wants him to just check it out. Reluctantly, Scottie agrees.
That night, Scottie sits at the bar at Ernie's and spies on Gavin's table, where he is sitting with his wife, Madeleine. He catches a glimpse of Madeleine, a beautiful woman in a green gown, as they leave the restaurant. The next day, Scottie waits outside their apartment building, hoping to catch a glimpse of her. At one point, she comes out and gets in a green car, and he follows her down an alleyway, where she parks and goes into a building.
Scottie follows, going into the building, a florist. Madeleine looks at the flowers, then picks out a small bouquet and leaves. Scottie follows her in her car, as she drives to a small church and goes in. Scottie follows her to the front of the church, where she goes out a side door to a small cemetery. There, she stands in front of a grave for a moment before leaving. Scottie goes to look at the grave, which is for a woman named Carlotta Valdes who died in 1857. He takes a note then goes to follow Madeleine once again.
Before we have any exposition about the characters or their relationships to one another, we see a high-energy suspenseful chase sequence. In the course of the chase, Scottie, the protagonist, nearly falls from a rooftop and watches as his partner, a policeman, falls to his death. This incident is highly affecting and causes Scottie to experience vertigo that, he comes to believe, makes it impossible for him to be a detective. We experience this traumatic incident as Scottie does; since it is at the beginning of the film, everything we remember about Scottie's history as a detective can be traced back to this one traumatic event.
The first relationship we are introduced to is the complicated friendship between Scottie and Midge. They are college friends who were once engaged, but now share a platonic intimacy that hovers around romance, but which never seems to gain traction in that direction. Midge tells Scottie that he's the only man for her, but he seems to remember that she's the one who called off the engagement. Then, when he asks her to drinks, she declines, insisting she has to work. Midge and Scottie seem to value their friendship more than they do any romantic or erotic spark, but it is unclear whether this makes either of them happy.
Vertigo and fear of heights are personal afflictions that do not necessarily seem so terrifying to the average viewer, yet Hitchcock is such a master of suspense that he manages to make Scottie's problem terrifying to the viewer. He does so primarily through his score and the camera angles. For instance, in the first sequence, we see Scottie from afar, hanging from the ledge of the building, before then seeing his face in close-up, and then his view of the height below him. We see him first from the perspective of the third person, and then closer, and then finally the camera takes his perspective, which effectually shows us his vertigo from a first-person perspective. Additionally, the score is exceedingly suspenseful and creepy, heightening the tension of the moment.
Soon after taking a break from being a detective, Scottie is contacted by an old college acquaintance who wants him to follow his wife. As Gavin Elster discusses the more supernatural elements of his wife's afflictions, Scottie is skeptical, but as soon as Scottie sees Madeleine, the woman in question, he is so taken in by her beauty and elegance that he decides to take the case. Madeleine is as mysterious as she is beautiful, seemingly in thrall to metaphysical forces, and it is this mystery that ultimately hooks Scottie.
Scottie proves himself to be the consummate detective, in spite of his initial misgivings about following Gavin's wife. Once he is on Madeleine's trail, Scottie is fully pulled in to her narrative, and even Gavin's suspicions that something occult may be at work. He chases Madeleine all over the city, from flower shops to cemeteries to museums, excited to be back on his beat, even if he swore he wouldn't go back to work for a while.