Building on the M. Night Shyamalan cinematic universe, Split introduces us to Kevin Wendell Crumb. He suffers from DID, but not just the movie style multiple personality silliness. This is going into the realm of superhumans, so when James McAvoy jumps from personality to personality and goes on and on about "the beast" and how it will do oh so much damage... yeah.. things get a bit more complex than you usual kidnapped horror...