| Director | M. Night Shyamalan |
|---|---|
| Budget | $9 million |
| Box office | $278.5 million |
Just outside Philadelphia, three teenage girls — friends Claire and Marcia, and their classmate Casey — are waiting in the car of Claire's father to be driven home from her birthday party. They are kidnapped by a man, who imprisons them in an underground lair. It becomes clear that this man has dissociative identity disorder (DID) rooted in his history of childhood abuse and abandonment. The man has been living with his 23 distinct identities ("alters") for several years with help from his therapist, Dr. Karen Fletcher, who is pleased that the man has been able to hold down a good job. One of these personas, "Barry", has been in control of deciding which personalities get to control the man's body; lately he has not allowed two others, "Dennis" and "Patricia", to have a turn due to the former's tendency to harass young women and the latter's belief in a mysterious 24th yet-to-manifest alter called "The Beast" who plans to rid the world of the "impure"those who have not suffered.
The captives meet "Patricia," who protects them from "Dennis" to save them for "The Beast," and a 9-year-old boy alter named "Hedwig," whom "Patricia" and "Dennis" manipulate to shut out the other alters. Through a series of flash-backs, it is revealed that Casey herself is a survivor of childhood sexual abuse. She attempts to psychologically manipulate the various alters to gain opportunities for escape. The captives make several escape attempts: one by climbing through an air vent, one by attacking the man with a chair, and one by finding a walkie-talkie and calling for help. The man punishes them for their failed escape attempts by locking them in separate rooms.
During a session, Dr. Fletcher questions the man about an incident where two teenage schoolgirls had placed his hands on their breasts during a field trip to his workplace, and becomes concerned when she realizes that "Dennis" has been impersonating "Barry." Dr. Fletcher goes to the lair to talk to "Dennis" and he confesses that he has met "The Beast". She discovers Claire, so "Dennis" incapacitates and imprisons Dr. Fletcher. "Dennis" goes to the train station and boards an empty train car, where "The Beast" takes over. "The Beast," who displays enhanced strength and animalistic tendencies, returns to his lair, thanks Dr. Fletcher for her help, and crushes her to death.
"The Beast" feeds upon and kills Claire and Marcia before approaching Casey. But Casey finds a note scrawled by Dr. Fletcher with instructions to call out the man's full nameKevin Wendell Crumbwhich brings forth his original personality. Upon learning of the situation and realizing that he has not been in control of his own body for two years, the horrified Kevin begs Casey to kill him with a shotgun he has hidden. This prompts all 24 personalities to fight for control, with "Patricia" the victor. She tells Casey that "Kevin" has been made to sleep far away and will not awaken now, even if his name is called. While "Patricia" returns control to "The Beast," Casey retrieves the shotgun and a box of cartridges and runs into a tunnel where "The Beast" stalks her. She locks herself in an iron cage and manages to shoot "The Beast" twice before running out of ammunition. Only wounded, he bends the iron bars with apparently superhuman strength but stops when he sees scars across Casey's abdomen and chestself-harm due to sexual abuse by her uncle and legal guardian, John, both before and after her father's death. "The Beast" tells Casey that because she has suffered, she is "pure" and he will spare her life. He leaves and she is found the following day by a worker. It is revealed that the lair is under the Philadelphia Zoo. Later, a police officer tells Casey her uncle has arrived to pick her up, but Casey hesitates.
In another hideout, "Dennis," "Patricia," and "Hedwig" discuss the power of "The Beast" and their plans to change the world. At the Silk City Diner, several patrons watch a news report on "The Beast's" crimes, with the correspondent mentioning that his numerous alters have earned him the nickname "The Horde." A waitress notes the similarity to a criminal in a wheelchair incarcerated 15 years earlier, who was also given a nickname. As she tries to remember it, David Dunn, sitting next to her, replies that it was "Mr. Glass."