The quiet suburb of New Salem is gripped by terror as a brutal serial killer is on the loose, abducting and torturing young women, keeping them captive for weeks before ultimately taking their lives. Among the latest victims is Aubrey Fleming, portrayed by Lindsay Lohan, a talented pianist and aspiring writer who mysteriously vanishes during a night out with friends. As the days pass, the special FBI Task Force assigned to the case grows more hopeless, fearing the worst for Aubrey.
Then, one fateful night, a driver stumbles upon a disheveled and critically injured young woman by the side of a deserted road. Rushed to the hospital, Aubrey's distraught parents, Susan and Daniel, played by Julia Ormond and Neal McDonough respectively, anxiously await her recovery as she drifts in and out of consciousness. When she finally regains her ability to communicate, she shocks everyone by asserting that she is actually Dakota Moss, a down-on-her-luck stripper, and that she has no recollection of who Aubrey Fleming is.
Her family and doctors, believing her to be suffering from post-traumatic stress disorder, can only hope that time and therapy will restore her memory. However, upon returning to her suburban home, Dakota maintains her identity, even though she bears wounds consistent with those inflicted upon the killer's previous victims. This deepens the FBI agents' confusion when they discover a story on Aubrey's computer featuring a character that shares Dakota's alter ego.
As Dakota begins to suspect that she might be Aubrey's identical twin sister, the truth comes tumbling out when Susan shows her a video of the pregnancy ultrasound, which reveals only one fetus. Confused and terrified, Dakota soon finds herself haunted by visions of a sinister figure brutally torturing a captive. With urgency pressing down on them for both Aubrey's and her safety, Dakota shares a staggering revelation with Daniel, propelling them into a frantic quest to find the monstrous killer.
Revelations unfurl as it is discovered that Aubrey and Dakota, born to Virginia Sue Moss, a crack addict, were separated at birth. Virginia gave birth at the same time the Flemings welcomed their own child, who sadly did not survive. Daniel Fleming, quietly raising one of the twins as his own, had been sending payments to Virginia over the years. After Dakota finds the envelopes indicating her past, she experiences the physical pain of her twin's injuries and is consequently found by the roadside.
Adding to their plight, the twins are revealed to be stigmatic twins, capable of sharing pain, communication, and even experiences—a connection that shines light on Aubrey's alarming accounts. In an attempt to uncover the truth, Dakota explores the grave of Aubrey's murdered friend, Jennifer Toland. There, she uncovers a blue ribbon linked to a piano competition, along with a message from Douglas Norquist, their piano teacher played by Thomas Tofel, leading Dakota to the horrifying realization that he murdered Jennifer and abducted Aubrey as retribution for their desire to quit piano training.
Confronting Norquist with Daniel, a deadly struggle ensues, resulting in Daniel's tragic death. However, Dakota manages to overpower Norquist, severing his hand and brutally stabbing him with his own blade. In a climactic moment of hope amid the horror, she uncovers Aubrey, who had been buried alive. The movie concludes with the two sisters lying side by side on the ground, gazing up at the night sky, united at last in survival.
