With "The Sixth Sense," "Unbreakable" and "Signs," writer/director M. Night Shyamalan has -- for better and worse -- become the king of twist endings. It's a reputation that makes his movies uniquely entertaining; because you know a perception-shattering twist is coming, anticipation is seeded ahead of even the first frame. So our review of Shyamalan's "Split" won't spoil the fun by giving away the big twist that critics and fans are loyally not talking about. Rather, we'll be discussing the plot, but nothing that hasn't been tipped in the trailers.

James McAvoy is on fire in a role from which this scene-chomping performer can really make a meal (see also "Victor Frankenstein"). Here he plays Kevin, a man suffering from Dissociative Identity Disorder, formerly known as Multiple Personality Disorder. While his therapist Dr. Fletcher (Betty Buckley) coaches Kevin to find a happy peace with the 23 alternate personalities within him, a trio of malevolent "alters" mastermind a wicked plan that involves abducting three teen girls from a mall parking lot, locking them away in a mysterious bunker so they may be "sacred food" for "The Beast."

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The film splits into four threads; the primary being the cat and mouse tale of Kevin and his captives, who desperately seek escape in between confrontations with his evil alters. The second is on the internal conflict of Kevin's personalities as they battle for control of his body. The third follows Fletcher as she traces the breadcrumbs the "good" alters drop as a cry for help. And the final focuses on the arc of quiet captive Casey ("The Witch"s Anya Taylor-Joy). While trendy cool girls Claire (Haley Lu Richardson) and Marcia (Jessica Sula) cry and propose "going crazy" on Kevin ambush-style, Casey goes still and silent, wading through flashbacks of formative hunting trips, presumably to find a more effective escape solution.

With so many plates spinning, perhaps Shyamalan thinks audiences won't notice all their wobbling. While shocking and occasionally intriguing, "Split" is not as clever as it believes it is. The central escape premise is sloppily structured, with no sense of build, and no suspense earned through seeding geography or a claustrophobic atmosphere. Most escape attempts simply involve a girl running through whatever opening presents itself until she's cornered and recaptured. Coming out in the wake of wildly praised escape movies like "Green Room," "Don't Breathe" and even "Room," "Split"s lack of development here stands out all the more, and squanders the problem-solving element that could have made this thriller truly tense. Instead, I spent the whole movie eyeing a glass vase established in the bunker bathroom, waiting for it to be broken and employed as a weapon. Spoilers: it won't be. It's just thoughtless set dressing.

Similarly frustrating are plot holes that defy simple logic. For instance, "good" alters repeatedly email Dr. Fletcher begging for emergency sessions. But again and again the evil alters show up to cover their tracks. So, why wouldn't the emailing alter just explain the situation, writing something like, "We've abducted those girls that are all over the news," or even just, "SEND THE POLICE!"?

Shyamalan gets so tangled in his DID fantasy that he neglects developing his characters. While McAvoy has plenty of personalities to play with, the rest of the cast is left to scrape stereotypes together with scraps of screen time. Buckley brings a lot of old-school brass to her determined doctor, but a flawed script has her making third act contortions that feel contrived and flat-out contradictory to Fletcher's pronounced beliefs about Kevin and DID.

Quick to suggest ambushing their attacker, Claire is deftly established as a fighter, but one setback sidelines and stagnates her. Marcia gets zero definition beyond being Claire's best friend, while Casey is chiefly defined by how she's not like the other girls. She's not wearing cute tights, short skirts and tight tops, but a body-shrouding flannel with lots of layers and jeans. So she's obviously a free-thinking, wounded misfit, right? The flashbacks that could give greater depth instead give way to disappointing reveals, more killer trees than seeing dead people.

To Shyamalan's credit, his captivating sense of wonder his films survives amid the mess. Rather than looking at DID as an affliction, he suggests perhaps it's a form of supernatural power. Through this angle, McAvoy is encouraged to go wild, manifesting an OCD brute, a pestering 9-year-old boy, a meticulous but merciless matriarch, and other colorful alters. But as more of Kevin's backstory and personalities are unveiled, "Split" feels less fun and more tragic. Kevin is a man in pain, acting out with violence. It's disturbing, not entertaining. Yet Shyamalan peppers the sequences of Kevin's menacing side with scenes where a child alter capers for laughs. We're essentially encouraged to mock the mentally ill, when we're not being urged to fear them. At best, it's ignorant; at worst, it's vile.

I lament "Split" is such a major misfire. After his banishment to director's jail for the abysmal "The Last Airbender," "The Visit" had me hopeful for the resurrection of Shyamalan greatness. Admittedly, it's always a jangled joy to see McAvoy cut loose in a big swing concept. But "Split" feels rushed and careless, spectacularly bungling a premise that had potential. Which makes its final reveal more frustrating than thrilling.

"Split" opens January 20.