The horror/thriller starts off with the kidnapping of three teenage girls,  Claire (Haley Lu Richardson) and Marcia (Jessica Sula) who are portrayed as the normal, popular girls, and the third teenager, Casey (Anya Taylor-Joy), is portrayed as the maverick and her story and history of sexual abuse is presented to us through short flashbacks throughout the movie.

We find out that the kidnapper is sexually abusive, has OCD and goes by the name Dennis–this is just one of the 24 different personalities.  Dennis masks his personality as another identity who goes by the name Barry, and regularly meets with his therapist Dr. Fletcher (Betty Buckley) more and more often as his internal conflicts magnify.  Dr. Fletcher notices small differences in “Barry’s” personality and begins to wonder if it is somebody else controlling the other personalities.

At the same time, Casey submits to Dennis’ demands while the two other girls try to fight him.  It is slowly revealed to us that Casey is actually analyzing the different personalities and uses this to her advantage.  As Casey slowly befriends one personality of a small 9 year old boy named “Hedwig”, She continues to gain insight on what Dennis’ big plan is.  She finds out it involves another identity called “the beast”.

Dr. Fletcher continues to meet with “Barry’s” unusual demands, she finds out that the two personalities Dennis and Patricia are the ones that are controlling all the other personalities.  They talk about if “the beast” is real and it is revealed that Kevin, the main, core identity of the 24, was left on the train by his father when he was little.

Dr. Fletcher races towards Kevin’s home as she reads a list of urgent emails from Barry.  She finds out about the beast’s plans and tries to escape, but is caught and drugged up.  Dennis then goes on a train and emerges as the beast, gaining superhuman strength and speed as he runs towards his home.  However Dr. Fletcher manages to write down Kevin’s full name and she is squeezed to death by the beast.

Casey escapes from her cell and sees the half eaten bodies of her friends and sees where Dr. Fletcher has been squeezed to death.  The beast comes for her but she reads the name Dr. Fletcher wrote down, forcing Kevin to take control of all the other identities.  Kevin directs her towards where the shotgun and shells are, and a chase ensues.  The Beast is impervious to the bullets and when he reaches her, he stops and sees scars all over Casey’s body, saying that she is pure.  She collapses and is rescued by a passing worker.

Shyamalan seems to portray a theme of naivety, and the idea of “what doesn’t kill you makes you stronger.”  The young Casey is exposed to abuse early on in life, learning about the real world the hard way, ultimately surviving the kidnapping.  However the two other girls, who seem to still be unscathed by any traumatic experience, end up dead when exposed to any sort of evil.  Dr. Fletcher is in a way naive too because she ignored that the different identities could be dangerous and involved in the kidnapping for so long.  She was also ignorant in the fact that the identities could have been deceiving her.

Split was received with some aggravation because of the way Shyamalan portrayed Dissociative Identity Disorder, further perpetuating the popular belief that individuals who suffer DID are extremely dangerous.