Complex sentence: The killer is revealed to be Toby, who was badly burned as a child after attending the showing of "Possessor" with his mother, who was a member of Gates' film cult and was killed in the fire.
Split into simpler sentences: The killer is revealed to be Toby, who was badly burned as a child after attending the showing of "Possessor" with his mother. Toby's mother was a member of Gates' film cult and was killed in the fire.