Dr. Carter Nix, portrayed by John Lithgow, is a highly regarded child psychologist whose life takes a harrowing turn. His wife, Jenny, played by Lolita Davidovich, is a devoted oncologist. As Carter temporarily steps away from his successful practice to focus on their two-year-old daughter, Amy, Jenny grows increasingly worried. She perceives that Carter’s attention towards their child has turned into an unhealthy obsession, as he treats her more like an experiment than a daughter.

As the story unfolds, it becomes evident that Carter is grappling with multiple personality disorder. His fractured psyche manifests in three distinct personalities: Cain, a cunning streetwise hustler; Josh, a scared and traumatized little boy; and Margo, a maternal figure. In a shocking twist, Carter and his persona, Cain, are involved in a series of murders targeting young mothers in a chilling pursuit of their children.

Amidst this turmoil, we learn about Jenny’s clandestine affair with Jack Dante, played by Steven Bauer, the widower of a previous patient. Their romantic history adds fuel to the fire as Jenny contemplates leaving Carter for Jack, who had once abandoned her. The situation spirals out of control when Carter unsuspectingly uncovers their secret rendezvous, plunging him further into madness. In a dark turn, Carter/Cain engages in a game of deception, leaving hints for the authorities that Jack is the true culprit.

The tension culminates when Carter attempts to murder Jenny by submerging her car in a lake. Though she manages to escape, she confronts him at their home, demanding to know her daughter’s whereabouts. Carter chillingly claims that Amy is with his deceased father.

As events unfold, Carter is arrested for attempted murder, leading to an interrogation by Dr. Lynn Waldheim, portrayed by Frances Sternhagen. Through hypnotherapy, she uncovers the disturbing truths behind Carter’s fragmented mental state. Dr. Waldheim reveals that she once collaborated with Carter’s father on a controversial book, Raising Cain, which explored the complex realms of multiple personality disorder. It becomes horrifyingly clear that Dr. Nix Sr. had subjected his son to trauma in an effort to document the emergence of his various personalities, eventually leading to Dr. Waldheim’s resignation from the case in horror at the unethical practices involved.

During the intense interrogation, the personality of Carter fades away, allowing Margo and Josh to take over. In a chilling rhymed recitation, Josh cryptically indicates the darkness that has enveloped their lives:

“Hickory dickory dock. Cain has picked his lock. He did a bad deed now Josh comes to bleed. Hickory dickory dock.”

As the police delve deeper, the identity crises continue, with Margo taking control and evading further questioning. In a dramatic escape, Carter, as both himself and Cain, overpowers Dr. Waldheim, masquerading as her to leave the facility undetected.

In a surprising twist, it’s revealed that Dr. Nix Sr. is alive and has been orchestrating a sinister operation from a hidden research facility in Norway, using his son to gather children for his experimental motivations. In a tense sequence, Jenny unknowingly follows Carter, disguised as Waldheim, only to stumble upon the truth with Dr. Nix Sr. and her daughter, Amy, in grave danger.

The film concludes with a poignant scene in the park, where Amy innocently calls for her “Daddy” while Jenny engages in casual conversation with another mother. As the tension mounts, Amy runs into the woods, beckoning for her father. When Jenny goes to embrace her, the chilling presence of Carter, in Margo’s guise, looms behind. The feeling of dread hangs heavily as Margo takes charge, leaving the audience in suspense about the future of Jenny and her child, unaware of the poisoned reality that surrounds them.