Casey Cooke (Anya Taylor-Joy), an introverted loner, gets a pity invite to the popular Claire's (Haley Lu Richardson) birthday party. When Casey, Claire, and Claire's best friend Marcia (Jessica Sula) are kidnapped by a strange, fastidious man (James McAvoy) in a mall parking lot, they soon learn that he has dissociative identity disorder. 23 different identities exist within the man (real-name Kevin), and while his childlike Hedwig and affable fashionista Barry seem good-natured, his icy matriarch Miss Patricia and fussy, menacing Dennis hint that a final, more sinister persona is about to emerge.
McAvoy does a fantastic job at adeptly portraying several different, unique characters, nailing different accents, body language and facial tics. Because of McAvoy, Kevin's "alters" are all distinctly recognizable from each other, so much so that the audience is eventually able to tell when one persona is imitating another. It's a performance that ranges from terrifying and empathetic to campy and absurd, over and over again. Taylor-Joy channels the same quiet intensity she showed off in last year's The Witch, and elevates Casey beyond the "depressed goth teen" archetype in a way that many other young actresses probably couldn't.
Split is both tightly framed and well lit, so we get a distinct sense of the claustrophobic basement the girls are held in. Cinematographer Mike Gioulakis, who Shyamalan hired after seeing his work in It Follows, brings the same creepy, dreamy, otherworldly feel to this film, and the subtle exploration of both captor and captive's repression and inner shame are echoed in its camerawork.
Shyamalan can't resist adding some of his less-effective hallmarks to Split, though; a protagonist with a past trauma who must overcome it later to defeat the villain, and a mythology that almost goes off the rails. We are told that Kevin has 23, possibly 24, different personalities, all with their own distinct personalities and habits, but we only meet a handful. This huge number seems like overkill when it doesn't hold any particular relevance to the story's plot. Shyamalan manages to reel in his tendency to let his stories overreach here though, so although Split veers close, it pulls itself in at the right moments.
On the subject of how it portrays mental illness, Split succeeds twofold: firstly, the character of Dr. Fletcher (portrayed with great warmth by Betty Buckley), Kevin's psychiatrist, has such honest compassion and sensitivity that we are aware that she deeply cares about her patients on a level beyond the therapist/client relationship. Because she views and treats them as human beings, the film never paints Kevin as a "monster" or a "magical madman," but a human being with a wide, complex array of characteristics.
The second reason why Split does a fair job at portraying mental illness is because, as the film goes on, viewers are made aware that something more paranormal is going on. While a bit of a silly stretch, this more fantastical element gives the film extra dimensions. So, though the final moments shoehorn in a hokey surprise, it's a fun nod to Shyamalan's past films and a much-needed breather — and, thankfully, not an ultra-serious twist ending. (Universal)