Single White Female is a 1992 American thriller based on John Lutz's novel SWF Seeks Same. The movie stars Bridget Fonda,and Jennifer Jason Leigh and is directed by Barbet Schroeder, who also did Reversal of Fortune.
Alison "Allie" Jones (Bridget Fonda) is a software designer in New York City. While her professional star is on the rise she has created a computer software package that will revolutionize the fashion world her personal life is a mess. Allie breaks up with her fiance, Sam Rawson (Steven Weber), after discovering that he slept with his ex-wife. Feeling unable to face the huge adjustment of suddenly living alone, Allie decides to find a roommate, and places an ad in the paper. Allie interviews a succession of candidates before settling on the shy Hedra "Hedy" Carlson (Jennifer Jason Leigh). Hedy quickly fills the void left in Allie's life by Sam's departure and their friendship deepens. However, Hedy is seen to be secretive, manipulative and disturbed. She erases Sam's phone messages when he calls to plead with Allie for a reconciliation. Before long, she even begins emulating the more sophisticated Allie in dress and manner. Allie passes off this strange behavior as that of an insecure but well-intentioned woman. When Allie reconciles with Sam, Hedy's obsession with Allie comes to the forefront. She kills the puppy she bought for Allie, making it look like an accident, and even has her hair cut and dyed to match Allie's look. More than a little unnerved, Allie goes into Hedy's room and looks through her possessions. She discovers that Hedy is not who she claims to be: Hedy's real name is Ellen Besch, and she witnessed her twin sister drown aged 9. Allie talks to her gay neighbor Graham, who advises Allie to get Hedy to move out of the apartment. Hedy overhears the conversation through the apartment's air vents and attacks Graham later that night, knocking him unconscious. Allie tries to talk to Hedy that night but Hedy's venom exposes itself as she calls Allie "fucking weak" for going back to Sam. Believing Sam will cheat on Allie, and that he is the real reason for Allie's cooling affections toward her, Hedy decides to trick him into infidelity by performing oral sex on him while he is half asleep, knowing he would mistake her for Allie. Afterward, Sam decides to confess to Allie, but Hedy kills him with a stiletto heel. In the morning Allie wakes to find Hedy feverishly cleaning the apartment, and is slightly moved that Hedy has decided to move out so quickly. When she sees a news report on Sam's death she realizes what has happened and tries to escape. Hedy takes Allie hostage at gunpoint in Graham's apartment, revealing the early morning cleaning was to erase any evidence that she existed, since only a handful of people knew she sublet the apartment. She intends to frame Allie for Sam's murder since any witnesses would assume they were the same person. Mitchell Meyerson (Stephen Tobolowsky), a client of Allie's who had nearly raped her, comes to the apartment looking for Allie; Allie had since erased all of Mitchell's computer files as a consequence of his actions. When Mitchell tries to free Allie from her bonds, Hedy attacks him and, ultimately, kills him. Allie is then left to fight for her life against Hedy, and after an exhaustive battle in the downstairs laundry room, she stabs Hedy to death with a screwdriver. Allie is then able to move on with her life; she forgives herself for Sam's death, using Hedy as the perfect example of the damage that survivor guilt can inflict upon someone. The film ends with a closeup of a photograph (assumed to have been made by Hedy), of the two women's faces superimposed as one.