context: A woman's face gives way to a kaleidoscope of credits, signalling the start of Alfred Hitchcock's Vertigo to Bernard Hermann's haunting score.A criminal climbs up the rungs of the ladder on a dark San Francisco night. John "Scottie" Ferguson (James Stewart), a detective, and a police officer are hot on his trail. They chase him across the top of buildings. The thief jumps between two buildings, making it across. The police officer follows, but Scottie can't get his footing. He slips. Scottie hangs on to the gutter as his fear of heights kicks in. The police officer tries to grab his hand, but he falls to his death. Scottie witnesses this and clutches the gutter.Months after the incident, Scottie reclines in the home of Marjorie "Midge" Wood (Barbara Bel Geddes), a painter and fashion illustrator. She is concerned about Scottie's plans now that he is back in shape. He has quit the police force due to his acrophobia, and does not want to be a desk jockey. Midge and Scottie used to be engaged back in college, but it was broken off. Scottie blithely waves their engagement off as a flight of fancy, ended by Midge, but it's clear from Midge's expression that Scottie was more likely the unwilling party and that Midge still holds a torch for him. She urges him to take a vacation. "Don't be so motherly", responds Scottie. They discuss an old college buddy, Gavin Elster (Tom Helmore), who wants to meet with Scottie. Scottie attempts to get over his fear of heights by using a step stool. He is able to handle the first two steps, but when he reaches the top, he looks out the window and panics. He collapses in Midge's arms.A familiar pedestrian crosses the street near the docks. Scottie meets Gavin, who is in the shipping business. Gavin married into the business, and he wants Scottie to tail his wife. He does not suspect infidelity, but hints that his wife has been possessed by something. She's become distant and distracted and has taken to roaming the city and surrounding area. The no-nonsense Scottie initially dismisses the supernatural undertones of Gavin's worries, but is nevertheless intrigued. Gavin tells Scottie to meet him and his wife at Ernie's Restaurant the following night.Ernie's Restaurant is a lavish, upscale eatery, plush and scarlet. Scottie first spots Madeleine Elster (Kim Novak) who is stunning, with platinum blonde hair and a green shawl. He is mesmerized by her.The next morning, he stalks her outside her house. She wears a simple gray suit with white gloves, as she gets into her green automobile. Scottie follows her through the streets of San Francisco, as she visits a flower shop and purchases a small bouquet. He then trails her to the Mission Dolores, where she goes through the chapel to the cemetery, finally stopping to stand at a grave. As she exits, Scottie notes the headstone, which reads "Carlotta Valdes born: December 3 1831 died: March 5 1857." He then tracks her to the Palace of the Legions of Honour, an art museum. Madeleine sits, staring at a portrait for hours. Scottie notices that the bouquet she purchased is just like the one in the painting. Also, her hair is done exactly like the woman in the painting. Scottie discovers from the curator that the painting is titled "Portrait of Carlotta." Finally, he follows her to the McKittrick Hotel, where Scottie observes Madeleine in a second story window. Scottie enters the old hotel and asks the manager (Ellen Corby), who the occupant of the room is. She hesitates to tell him, until Scottie reveals his badge. The manager reveals that the woman's name is Carlotta Valdes, but that Miss Valdes has not been in the room all day. Scottie finds this impossible, and goes up to the room, which is indeed empty. He looks down the street to discover that her car is gone.Scottie returns to Midge's home where she tells him of San Francisco historian Pop Liebel (Konstantin Shayne), who owns the Argosy Book Shop. She and Scottie pay Pop a visit and Scottie asks the man about the McKittrick hotel. Pop tells Scottie that the hotel was originally a house built by a rich man for his mistress, Carlotta Valdes, and they had a child. However, the rich man eventually discarded Carlotta, keeping their child to raise with his childless wife. Carlotta went from depressed to insane, and finally took her own life.On the drive home, Midge and Scottie talk about the portrait; he shows her the catalogue picture. The resemblance is uncanny. Another conversation with Gavin reveals that Madeleine had started to wear Carlotta's jewellery, particularly a ruby pendant shown in the painting. Madeleine's great-grandmother was Carlotta Valdes, a fact that Madeleine does not know. Gavin only knows this fact because Madeleine's mother told him.Scottie follows Madeleine the next day to the Palace of the Legions, where she gazes at the portrait. Then he follows her to Fort Point near the Golden Gate Bridge. Madeleine strolls by the shore, throwing petals into the bay, until without warning, she jumps in. Scottie dives after her. She is alive but unconscious, and he takes her back to his apartment.Madeleine wakes up at Scottie's apartment, perplexed and alarmed to find herself naked in a strange man's bed. Scottie hands her a red bathrobe and explains that he rescued her from drowning. Madeleine maintains that she must have fainted and fallen. He questions her, "Has this ever happened to you before?" Gavin calls, concerned about the whereabouts of his wife. Scottie reassures him that Madeleine is at his apartment. Gavin informs Scottie that Madeleine is twenty-six - the same age at which Carlotta Valdes committed suicide. Scottie hears the door close, and realises that Madeleine has left. As Madeleine drives away from Scottie's house, Midge arrives just in time to have a misunderstanding. She believes that Scottie and Madeleine are in a relationship.The next morning, Scottie trails Madeleine through the streets of San Francisco, only to find that Madeleine has been looking for Scottie's house. Scottie catches her leaving a thank you letter for saving her. She did not know the address, but followed the Coit Tower. Scottie, now smitten with Madeleine, insists that they wander together, because they are both alone.They arrive at Big Basin Redwoods State Park, where they admire the ancient redwoods. As they view a cross-section of a tree with the approximate dates of historical events, Madeleine goes into a trance, seemingly becoming Carlotta, recounting the dates of her birth and death. Madeleine wanders deeper into the woods, and Scottie follows her. He confronts her about her jump into the bay, and tries to bring Madeleine back. By the shore, Madeleine begins to reveal fragments of her vague memories: an empty grave with no name, waiting for her; an empty room in which she sits alone; and finally a tower, bell, and garden in Spain. Madeleine admits she is not crazy; she does not want to die. They kiss as the waves crash onto the rocks. Scottie promises he will never leave her.Scottie arrives at Midge's place upon having received a note from Midge inquiring as to his whereabouts. Midge mischievously reveals a new picture she's been painting-- a portrait of herself as Carlotta Valdes. Scottie is not amused by the gag. Distressed, he leaves immediately. Midge ruins the painting, upset by the depth of his feeling for Madeleine and her own misguided attempt to make light of it, which has distanced them further.Madeleine returns to Scottie's house, where she tells him of an awful dream, with a tower, a bell, and a village. As she describes the location in detail, Scottie finishes her descriptions. "You've been there!" he exclaims. Scottie is talking about the San Juan Bautista, a mission that has been converted into a museum. They drive to the mission.When they arrive at the mission, they enter the livery stable, where Scottie tries to dismiss the dreams logically. He points out certain objects that are real. They kiss. Madeleine explains she must do something. She asks him if he believes she loves him. He replies yes. "And if you lose me, then you'll know I, I loved you. And I wanted to go on loving you,'' she says. She starts to go to the church, when Scottie realizes she is going to the bell tower. Scottie chases her into the chapel, and sees her run up the stairs. He follows her, but as he looks down, his vertigo sets in, paralyzing him. He cannot follow her up to the top of the bell tower. He watches, helpless, in fear and horror as Madeleine's body plunges to the tiles below. Scottie staggers out of the mission, sun blinding his eyes, dumbfounded.At the a judicial hearing concerning Madeleine's death, the judge is particularly cruel to Scottie; he insults him for letting his weakness get in the way of saving Madeleine. The court rules the incident a suicide. Gavin comforts Scottie, while telling him that, with the loss of his wife, he can no longer stay in San Francisco. Gavin sets off for Europe.Scottie has trouble sleeping. Blue and purple flashes signal his nightmare, as an animated bouquet unravels. He dreams of seeing Carlotta Valdes at the hearing, with special emphasis on the ruby necklace. Scottie walks into the cemetery where there is an open grave. Scottie falls into the grave, which has become precipitous, then his body lands next to Madeleine's on the tiles of the mission. He wakes up in a cold sweat.Midge arrives to care for Scottie in a psychiatric ward. She tries to comfort him, "mother's here." Scottie will not speak, he is in a daze. The doctor believes that Scottie will be incapacitated for a year due to stress and anxiety from his depression and guilt.Upon his eventual release from the hospital, Scottie remains in the grip of an obsession. He visits the old Elster home, and spots the green car. In the distance, a woman in gray suit is getting in it. Unfortunately for him, it is not Madeleine; it is an old neighbour who bought the car from Gavin. At Ernie's he spots a woman in a green evening dress, but again, it is not Madeleine. He even sees Madeleine at the Palace of the Legions, but once again, it is not her. While looking at a bouquet at a flower shop, he sees a striking brunette in a green suit. Although she doesn't resemble Madeleine in dress, style, or movement, the face is a dead ringer. He follows her to the Hotel Empire, and sees her through the fifth floor window.When Scottie knocks on the door, the woman is concerned that he is a creep. He reassures her he just wants to talk. He interrogates her rather aggressively, and she shows him proof that she is Judy Barton (Kim Novak again) from Salina, Kansas. Judy realises that Scottie's heart is broken for his former flame, and she takes pity on him. She agrees to go for dinner with him at Ernie's.After Scottie leaves, flashbacks reveal Judy's memories. She was Madeleine, running up the steps of the bell tower. At the top, Gavin Elster was there, holding the body of the real Madeleine Elster, dressed in exactly the same outfit as Judy. It was the real Madeleine's body that was thrown off the bell tower, with Judy letting out the scream. Judy even keeps the gray suit that she wore as Madeleine Elster hidden in the back of her closet. She begins to write a letter to Scottie, explaining that she was Gavin's accomplice in the murder of his wife. She had become her doppelgänger to fool Scottie, and use him as a witness to lend credence to the idea that Madeleine was mentally unstable. Gavin had known about his vertigo, and knew that Scottie would never make it to the top of the bell tower. Judy reconsiders this letter, and tears it up.That night, Scottie suspects he sees Madeleine at Ernie's. He escorts Judy home, her apartment flooded with the green neon light of the Hotel Empire sign. He's overwhelmed by his yearning for Madeleine, a woman lost to him, although through Judy he is able to capture the ghost of Madeleine's presence. They agree to meet the next morning.They engage in a series of dates, with Scottie becoming happier with the relationship. However, little by little, he begins to make Judy over in the image of Madeleine. He searches obsessively for the gray suit and white gloves that Madeleine used to wear and even convinces Judy to bleach her hair. Although Judy begs him to love her for herself, she has fallen so in love with Scottie that she allows him to change her into the other woman.After undergoing an extensive makeover, Judy returns to an anxiously awaiting Scottie. Scottie won't brook the slightest deviation from his recreation of Madeleine, and insists that Judy pin her now platinum blonde hair up exactly the way Madeleine wore hers, which she does, completing the transformation. In a dreamlike state, with the green glow all around them, they embrace and kiss. The room turns into the livery stable from the Mission, Scottie's last kiss with Madeleine, and then back to the apartment. Scottie has finally managed to turn back time and resurrect Madeleine from the dead.A couple of nights later, the two decide to go out to Ernie's. Judy dresses up, and wears the same ruby pendant depicted in the portrait of Carlotta. Scottie realizes that something is amiss. He suddenly becomes distant. He passes Ernie's and continues driving past the redwood forest. He tells her he has one final thing to do. Judy is torn between her love for Scottie and the fear and guilt she feels over having colluded with Gavin Elster to dupe Scottie. They arrive at the mission, where Scottie forces Judy to re-enact Madeleine's last moments; their final kiss, Madeleine's parting words. He relentlessly pushes Judy up the stairs of the mission tower, discovering in the process that he's conquered his vertigo. He reveals to Judy that her necklace gave her away.As he reaches the top of the bell tower, he puts the whole puzzle together. He realizes that Judy was the counterfeit all along. He never knew the real Madeleine Elster. He was being set up as Gavin Elster's witness in the murder of Elster's wife. He pulls Judy to the top of the tower, where she protests. Judy pleads that she has fallen in love with Scottie. They kiss. The sudden appearance of a nun, however, startles Judy, who steps backwards and plummets to her death off the ledge. As the nun tolls the death bell, a devastated Scottie stands frozen in despair, having now lost the same woman twice, and this time, forever.
question: Who  asks Scottie to follow his wife, Madeleine, claiming she has been possessed?
answer: Gavin Elster