Three weeks after the events of Split, David Dunn (Bruce Willis) works with his now adult son Joseph in using his superhuman abilities to protect people from criminals under a new alias known as "The Overseer". David learns from Joseph that Kevin Wendell Crumb (James McAvoy), who suffers from dissociative identity disorder which provides his moniker "The Horde", has a group of cheerleaders up in a warehouse. David goes to free them but encounters one of Kevin's personalities known as "The Beast," and the ensuing fight spills out into the streets. The Philadelphia police department are called leading to the eventual capture of both David and Kevin. The two are sent to a mental institution where Elijah Price (Samuel L. Jackson), David’s sworn enemy who is also known as "Mr. Glass", is being held.