When your memory has been taken, who do you trust?

While driving at night along the San Francisco coast, architect Dan Merrick (Tom Berenger) and wife Judith (Greta Scacchi) are involved in a violent car wreck. Dan suffers major injuries and significant brain trauma, resulting in total amnesia. After extensive plastic surgery, Dan returns home in Judith's care.

Dan relies on those close to him to help him restore his past, including his business partner Jeb Scott (Corbin Bernsen) and Jeb's wife, Jenny (Joanne Whalley Kilmer). While recovering, Dan has frequent flashbacks of imagery he believes to be events that led up to his fateful car crash.

Dan finds discrepancies in the stories about his "former self." He stumbles upon photographs showing Judith sleeping with another man. At his office, Dan finds an expensive bill he paid to a pet store and follows up by visiting its proprietor, Gus Klein (Bob Hoskins). Gus informs him that the payment was actually for services provided as a private investigator. Gus says he was hired by Dan to follow his Judith and that his investigation had revealed she was indeed cheating on him with a man named Jack Stanton (Scott Getlin).

Judith arranges a meeting with Stanton, which Dan overhears. He follows her. Judith stops at the site of an old shipwreck slated for removal by Dan's company to make way for a real estate development. Assuming the wreck is a key in remembering his past, Dan has its removal postponed.

Jeb's wife Jenny accuses Judith of planning the accident to eliminate Dan. As he works with Gus to keep tabs his wife with a wiretap, Dan tails her to a hotel where she and Stanton are to meet. but Stanton leaves and a chase ensues through a heavily wooded area. After gunshots are fired from Stanton's car, Dan and Gus crash while Stanton escapes.

That night at home, Dan arms himself and lies in wait. At gunpoint, an intruder is revealed to be Judith disguised as Stanton. She explains that Stanton is actually dead, killed by Dan on the night of the accident. According to Judith, she had intended to stop the affair with Stanton, but Dan murdered him before knowing this.

Judith says she and Dan decided to cover up the murder by disposing of Stanton's body in the shipwreck. When Dan reveals he postponed the ship's removal, Judith becomes hysterical and suggests they both should flee.

Dan receives a frantic phone call from Jenny imploring him to see her. Upon arriving, Dan finds Jenny dead. He is confronted at gunpoint by Gus, who now thinks Dan must have murdered Stanton. Pleading for his life, Dan convinces Gus to visit the shipwreck.

There they find a chemical storage container. Dan dredges up a body of a man who looks exactly like himself—Dan Merrick. In a moment of clarity brought on by this shocking development, Dan suddenly realizes he is not Dan Merrick—he is, in truth, Jack Stanton.

Flooded with flashbacks, Jack pieces together the real events that led up to the accident: An abusive Dan confronted his wife Judith with evidence of her infidelity. She called for help and Jack raced to her home, arriving moments too late to prevent her from shooting her husband. Jack wanted to go to the police, but Judith convinced him to cover up the murder and hide Dan's body. After doing so, Jack told Judith he wanted out of the relationship. This angered and distracted Judith, who drove the two into the spectacular car wreck.

Judith had banked on the chemicals in the ship dissolving Dan's body, but because it was actually Formaldehyde, she had actually preserved it. Gus observes this and is shot by Judith, who had followed them. Judith now forces Jack to leave with her at gunpoint. She drives erratically down the same stretch of road the two did the night of the accident.

She claims she hid the facts from Jack so he'd have plausible deniability. After the crash, plastic surgeons simply assumed the man she was with was her husband Dan, so she went along with this. Distracted by a police helicopter, Judith loses control of the gun. Out of options, Judith decides to kill both of them in a suicidal car crash. Jack rolls out at the last second, while she plummets to her death on the shoreline below.

The police helicopter lands, and an injured—but alive—Gus Klein emerges, calling out to Jack as "Dan," asking if he's all right. Jack doesn't correct him.