This is a timeline of events that occurred in 2016.
- Kidnapping of Casey, Claire and Marcia: Claire, Casey and another friend, Marcia, went to have some shopping with Claire's father taking them. As they ended and returned to the car, the Philadelphia zoo worker who is having psychotic nature and severe personality disorder, Kevin Wendell Crumb, appeared as one of his own 24 identities; Dennis, a tough and manipulative pedophile. Dennis attacked Claire's father, and entered into the car. Then, Casey and her friends were sprayed by him with a special sleeping gas. The three girls awakened at a room of a secretive house. Dennis entered into the room and took up Marcia but not before Casey told her to behave herself even if it was an unexpected violent assault. Outside the room, Dennis wanted Marcia to dance for him, and he sexually harassed her. Marcia managed to prevent him from doing it by biting him in the hand, causing Dennis to leave Marcia in the room.
- Kevin has been treated by his psychiatrist Dr. Karen Fletcher, and appears stable: within his mind, all of his personalities sit in chairs in a room, waiting for their turn "in the light, while "Barry" controls who gets to go in the light. Two personalities, "Dennis" and "Patricia", are kept out because of Dennis's voyeuristic tendencies and obsessive–compulsive disorder, and both personalities' worshiping of "The Beast", a rumoured 24th personality.
- The three girls realize Kevin's nature when they meet "Patricia", who dresses as a woman. Casey seeks to befriend "Hedwig", a personality that claims to be a nine-year-old boy, who confides that the girls will be sacrificed to "The Beast". He says that he stole control over the light from "Barry" and was persuaded to help "Dennis" and "Patricia". When Claire attempts to escape, "Dennis" locks her in a separate cell.
- "Dennis" masquerades as "Barry" and attends a meeting with Fletcher, but she realizes that "Dennis" and "Patricia" have supplanted "Barry" as the dominant personality.
- Marcia tries to escape next but is caught and also placed in a different cell. Later, Casey continues to befriend "Hedwig", having earlier heard him mention a window in his bedroom is only a drawing of a window. She radios for help but is subdued by "Patricia".
- Ritual of The Beast: Fletcher suspects Kevin is responsible for the kidnappings. She discovers Claire at Kevin's house but is caught, drugged, and locked up by "Dennis", who then becomes "The Beast", manifesting superhuman speed, strength, and agility. Knowing that the only way to call to the real Kevin is to speak his full name, Fletcher writes it on a piece of paper before being killed by "The Beast". Returning to his hideout, 'the Beast' confronts Dr. Fletcher. She tries stabbing him with a knife, but the knife shatters. The Beast then murders her, demonstrating incredible physical strength. He then proceeds to savagely kill Marcia and then Claire, while Casey stumbles upon Dr. Fletcher's corpse as well as her instructional note.
- Escape from the Philadelphia Zoo: "The Beast" begins to bend apart the bars of the cage in which Casey has locked herself, but then notices numerous old, faded scars on her shoulders and lower torso. He then rejoices in the fact that she is "pure". Concluding that troubled people are exceptional, "The Beast" spares Casey's life and leaves. Casey is rescued by one of Kevin's coworkers and learns she was being held underneath the Philadelphia Zoo, where Kevin worked and lived.
- Casey is asked by a police officer if she is ready to return home with her uncle. She hesitates, and her final response is not shown.
- In another hideout, "Dennis", "Patricia", and "Hedwig" exert collective control over Kevin's body and admire the power of "The Beast" and their plans to change the world.
- In a diner, patrons listen to the media coverage of Kevin's crimes, for which he has been nicknamed "The Horde". One of the patrons notes the similarity between Kevin and a terrorist who uses a wheelchair and was arrested 15 years prior. The man sitting next to her is revealed to be an older David Dunn, who reminds the patron that the terrorist's name was "Mr. Glass".