Struggling screenwriter Charlie Baxter sets out to write his long-blocked 'great American screenplay' when he suffers a heart attack and his mysterious upstairs neighbour 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.