This is one of the first official ripoffs of “The Exorcist”.It actually tried to rip off that AND “Rosemary’s Baby”.The 1975 American release was called “Beyond The Door”, while in England it was titled, “The Devil Within Her” a year earlier..This was actually a big money maker in 1975!Right behind “Jaws”.
Just bought a shiny new copy of “Beyond the Door” at HMV (Bit pricey but worth it). Have the in-name-only sequel “Shock” (BTD II) by Bava which is also worth a look. “Beyond the Door III” is on ebay. Pity “Passions” didn’t utilize the “Beyond the Door” material for the Mills/”Tabitha” charactor. They were just getting into “Dark Shadows” mythology by having “Tabby” date “Barnabas Collins” when the soap got cancelled (again). With all the supernatural mayhem going on in “Harmony”, “Beyond the Door” would have made wonderful backstory.