Director M. Night Shyamalan returns to eerie-good form with Split, a creepy suspense thriller elevated by James McAvoy's chilling, first-rate performance as a man afflicted with dissociative identity disorder, or split personalities. McAvoy's Kevin has 23 distinct alternate personages already bouncing around in his head, with a 24th -- stronger and more menacing than the others -- threatening to emerge. Dennis, one of Kevin's more dominant personas, kidnaps three high-school girls from a suburban Philadelphia mall and locks them in a threadbare basement that's equipped with a blindingly clean bathroom (Dennis is a germophobe); he then informs them that they are "sacred food" to be sacrificed to a soon-to-arrive beast. Two of the girls, besties Marcia (Jessica Sula) and Claire (Haley Lu Richardson), are, understandably, scared out of their minds. But outsider Casey (Anya Taylor-Joy) takes a more measured approach to their predicament, the reason for which is revealed in a series of flashbacks to her troubled childhood. When the trio discover that their abductor has multiple personalities, Casey decides to pit one of them, a sneaky nine-year-old boy named Hedwig, against the others in the hope of tricking him into helping them escape. What the girls don't see are Kevin's visits to his psychiatrist, Dr. Karen Fletcher (Betty Buckley). Kevin talks to her as Barry, a flamboyant fashion designer who claims everything is fine, but his constant email requests for appointments are taken by Fletcher as a dire warning that he is hiding some heinous act he has committed, but can't quite bring himself to confess. As Fletcher delves deeper into Barry's activities and the girls get closer to escaping, Shyamalan ratchets up the suspense to a nail-biting degree, and concludes his horror show with a clever twist that will put a smile on the faces of his many fans who have longed for a comeback after a string of critical and box-office duds (After Earth, The Last Airbender, The Happening, etc.). Split benefits greatly from Mike Gioulakis' dark, foreboding cinematography and Shyamalan's tight, efficient script and direction, but most of all from its pitch-perfect cast. Taylor-Joy, so good in The Witch, is an actress bound for stardom; when she's onscreen, it's impossible to look away. Casey is no mere teen in peril but a damaged soul, and Taylor-Joy makes us feel every inch of her pain. One of Kevin's personas tells her, "The broken are the more evolved," and so Casey draws strength from the deep well of heartbreak inside her in order to survive. Sula and Richardson are effective in limited, underwritten roles, and Buckley brings great warmth to Fletcher that helps us see Kevin and his alter egos as real people with whom we can sympathize. But McAvoy is the real standout here. His role could easily have descended into camp, but he treats each of Kevin's personalities with great respect, thus making them believable. He shifts, seemingly effortlessly, from one persona to another in an instant by altering his facial expressions and voice. The performance is a killer. As is the movie.