Catherine Deane (Jennifer Lopez) is a psychologist dedicated to developing a revolutionary new therapy to reach into the unconscious mind. Though she intends her work to be used to bring traumatized children back to a normal life, her technique catches the eye of FBI Agent Peter Novak (Vince Vaughn), who would like her to use it for a much different purpose. Novak has been pursuing serial killer Carl Stargher (Vincent D'Onofrio), whose M. O. is to kidnap women, lock them in a glass enclosure, and then slowly drown them. When Novak finally tracks down Stargher, he has fallen into a comatose state and cannot tell Novak where his latest victim is being held. In a desperate attempt to save the last woman kidnapped by Stargher, Agent Novak asks Deane to use her technique to enter the killer's mind and determine where she is being held. She takes on the challenge, entering the strange and dark world inside the mind of a killer, in the hopes that they can save his intended last victim in time.