In SPLIT, teen birthday girl Claire (Haley Lu Richardson) is finishing up a party with her friend Marcia (Jessica Sula). But her “mercy invite,” troubled Casey (Anya Taylor-Joy), can’t find a ride home. Claire’s dad prepares to drive them, but then a mysterious man (James McAvoy) kidnaps all three girls and locks them in a windowless room. They notice that he acts strangely, showing different personalities and holding conversations with himself. Unbeknownst to the girls, the man goes to see his therapist, Dr. Fletcher (Betty Buckley), who tries to communicate with his 23 personalities. But he warns her of the coming of “the Beast,” an all-powerful monster that could be a twenty-fourth — and who might just have an appetite for teen girls.