The movie opens with the murder of a co-worker in New York City, in which the protagonist, Holly, is implicated. She decides to leave the city and move to Los Angeles in an attempt to start a new life and escape her past. However, she soon starts experiencing strange occurrences and delusions that suggest she is being followed by her doppelganger, a sinister version of herself.
Holly finds a room for rent in a cozy house owned by a charming but eccentric writer named Patrick, who becomes infatuated with her. They start a passionate affair, but Patrick begins to notice bizarre and unsettling changes in Holly's behavior. He wonders if her double is real or if it's all in her mind. As he delves deeper into Holly's past, he learns that she has a history of mental illness and he begins to question his own sanity.
The two worlds—Holly's reality and her doppelganger's dark, twisted world—start to collide, and Patrick becomes trapped in a dangerous and unpredictable love triangle. As he fights to protect Holly from her own demons, he must also face his own inner demons and fight for his own sanity. In the end, the truth behind Holly's madness is revealed, and Patrick must decide whether to stay with her or save himself from her dangerous alter-ego.