The synopsis: A group of people become stranded at a motel during a massive storm, and are gradually murdered one by one by an unknown serial killer.
The twist: None of it is real, and none of it ever actually happened. The people in the motel are simply split personalities in the head of a real-life serial killer, whose psychiatrist created this fictional scenario to "kill off" his violent personalities, in hopes of leaving a kinder man in his wake.
The amount of damage it'll do to your psyche: 🔪🔪