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Struggling screenwriter Charlie Baxter sets out to write his long-blocked "great American screenplay" when he suffers a heart attack and his mysterious upstairs neighbor Doctor Shockner comes to his rescue. The doctor persuades Baxter to stay until he recovers fully, and introduces him to a nightmarish world of insane experiments and murder. Baxter knows something must be done to stop the evil that resides in the room at the top of the stairs.