Margaret "Marnie" Edgar (Tippi Hedren) steals $10,000 from her employer's company safe and flees. She had used her charms on Sidney Strutt (Martin Gabel), a tax consultant, to get a clerical job without references. After changing her appearance and identity, she makes a quick trip to a horse stable in Virginia, where she keeps a horse named Forio, and then to Baltimore for a surprise visit to her mother, Bernice (Louise Latham). Though Bernice seems to care more for a young neighbor named Jessie than she ever did her own daughter, Marnie shows her love for her and gives her money.Mark and Marnie on their honeymoon cruiseWhen Mark Rutland (Sean Connery), a wealthy widower who owns a publishing company in Philadelphia, sees Strutt on business, he learns of the robbery. He recalls Marnie from a previous visit. Unaware of this, Marnie applies for a job at Mark's company; intrigued, he hires her as a typist, and they see each other socially. When Marnie has a panic attack during a thunderstorm, he hugs her and quietly kisses her. Marnie also has bad dreams and a phobia of the color red.Marnie repeats her crime at Markâs company, stealing a large sum of money and fleeing. Mark tracks her down at the horse stable where she keeps Forio. Shockingly, he blackmails her into marrying him.They marry, much to the chagrin of Mark's former sister-in-law, Lil (Diane Baker), who has had an eye on him ever since her sister's death. Lil learns that he is spending extravagantly on Marnie and becomes suspicious. On her honeymoon cruise, Marnie admits to Mark that she cannot stand to be touched by a man. Mark starts to respect her wishes, but then rapes her. The next morning, she tries to drown herself in the ship's pool, but Mark gets there in time to save her.Upon their return home, Mark discovers that Marnie's mother is still alive; he hires a private investigator to find out all he can about the woman. Meanwhile, Lil overhears that Mark has "paid off Strutt" on Marnie's behalf, so she mischievously invites Strutt to a party at Mark's house. There, a furious Strutt recognizes Marnie, but does not expose her after Mark threatens to take his business elsewhere. When Marnie later admits to additional robberies, Mark offers to pay back all her victims to keep the police away.Invited to ride in a fox hunt, Marnie enjoys herself, but becomes perturbed when the hounds corner the fox and begin to pull it from its den. When another rider wearing a traditional scarlet coat comes into view, her phobia kicks in and she bolts on her horse Forio. After a wild gallop, the horse falls and suffers a catastrophic injury, forcing Marnie to shoot him. Crazed with grief, Marnie goes to Mark's office to rob his safe again, but this time, she cannot bring herself to do it. Mark surprises her and eggs her on to take the money, but still she cannot.He then takes Marnie to Baltimore to see Bernice. Mark confronts Bernice about her past as a prostitute, and demands the truth. When Bernice attacks Mark hysterically, Marnie's long-suppressed memories suddenly surface. She remembers that when she was a child, a drunken sailor (Bruce Dern), one of Bernice's clients, had tried to comfort her during a thunderstorm. Bernice, thinking he was molesting Marnie, attacked him. Frightened, Marnie struck him with a fireplace poker and killed him. Bernice calmly admits everything, and she tells how she got Marnie, and how much she has always loved her.Now understanding the source of her fears, Marnie asks Mark what to do; he lets her know that he is on her side and will defend her. She responds, "I don't want to go to jail; I'd rather stay with you.", Question: Who is Mark's former sister-in-law?
Output: Answer: Lil