Three adolescents, Claire, Marcia and untouchable Casey, are abducted and held hostage by 'Dennis', one of 23 identities show in the brain of Kevin Wendell Crumb, a casualty of adolescence mishandle determined to have dissociative personality issue. Throughout the years, Kevin has been dealt with by his specialist Dr. Fletcher, and seems stable: the majority of his identities sit in seats in a room, sitting tight for their turn 'in the light', i. e, controlling the body, while 'Barry' controls who gets the chance to go in the light. Two identities, 'Dennis' and 'Patricia', are kept out. For Dennis' situation, this is on the grounds that he has both voyeuristic inclinations and obsessive–compulsive issue.

The three young ladies understand Kevin's inclination when they meet 'Patricia', who dresses as a lady. Casey tries to become friends with 'Hedwig', an identity that cases to be a nine-year-old kid, who trusts that they will be yielded to 'The Beast', a supposed 24th identity. At the point when Claire endeavors to get away, 'Dennis' secures her a different cell. 'Dennis' takes on the appearance of 'Barry' and goes to a meeting with Dr. Fletcher, yet Dr. Fletcher rapidly acknowledges 'Dennis' and 'Patricia' have supplanted 'Barry' as the prevailing identity.

Marcia tries to escape next yet is gotten and furthermore put in an alternate cell. Casey keeps on become a close acquaintence with 'Hedwig', having prior heard him say a window in his room. 'Dennis' and Dr. Fletcher discuss Kevin's dad, who surrendered Kevin as a kid. The identities started showing to help Kevin adapt to the manhandle he was subjected to by his mom, who experienced obsessive–compulsive issue. Casey influences 'Hedwig' to take her to his room, yet she is troubled to discover that the 'window' in the room is just a drawing of a window.

She radios for help however is stifled by 'Patricia'. Casey encounters flashbacks of being attacked by her uncle John, who turned into her legitimate watchman after her dad's demise. Dr. Fletcher speculates Kevin is in charge of the kidnappings. She finds Claire at Kevin's home yet is gotten, tranquilized, and bolted up by 'Dennis', who then turns into 'The Beast', showing superhuman speed, quality, and deftness. Realizing that the best way to call to the genuine Kevin is to talk his full name, Dr. Fletcher composes it on a bit of paper before being slaughtered by 'The Beast'.

'The Beast' executes and tears apart Marcia, then Claire, while Casey unearths Dr. Fletcher's carcass and her note. She quickly calls Kevin to 'the light' by talking his name. Stunned by his activities, Kevin orders Casey to slaughter him before his different identities start to assume control. As 'The Beast' returns, Casey shoots and harms him just externally. 'The Beast' voices his arrangements to free the universe of the 'untouched', those whose hearts are polluted in light of the fact that they have never endured in their lives.

Harmed however he might be, 'The Beast' still seems equipped for tearing open the substantial obligation way to the confine in which Casey has bolted herself when he sees various old, blurred scars on her lower middle. He then cheers in the way that she is 'unadulterated'. Presuming that harried individuals are uncommon, 'The Beast' chooses to extra Casey's life. Casey is at last saved by one of Kevin's associates and learns she was being held underneath the Philadelphia Zoo where Kevin worked and lived. Casey is asked by a cop in the event that she is prepared to return home with her uncle. She dithers, and her last reaction is not appeared.