In the wake of the massive box office success of THE EXORCIST (1974), it was a given that a legion of cash-ins and ripoffs would soon follow, and from what I recall at the time this Italian-American effort was by far the most prominent of that misbegotten lot. And though the film itself is about as scary as a sink full of tepid dishwater, it does gain points from me for having the sheer balls to rip off both THE EXORCIST and ROSEMARY'S BABY (1968) at the same time. To tell the truth, BEYOND THE DOOR really works more as a ROSEMARY'S BABY knockoff than a flat-out swipe from THE EXORCIST but any way you cut it, a ripoff is still a ripoff.
Long story short: A woman (Juliet Mills) is pregnant with her third child and in this case the third time is definitely not the charm. With her pregnancy marked by the usual laundry list of demonic possession movie tropes, it soon becomes apparent that she is either possessed by a demon/Satan or she's carrying the Anti-Christ, or maybe both. That's all you really need to know, because BEYOND THE DOOR just isn't really all that interesting or even entertaining. I remembered it as being such from my long-ago days of watching movies en masse while drunk or stoned (or both, if truth be told) but I opted to watch it for this year's 31-day overview and give it a fair second chance, but I'm sorry to say that it was every bit the dud I remembered it being. It even ends on the always-eyerolling "THE END...QUESTION MARK?" note, which made me want to punch my TV right in the screen. This one's strictly for devil junk completists only, and maybe even that audience would be advised to give it a miss. It's simply mediocre, not even bad enough to do a one-eighty on itself and become fun as a bad movie that one can derive some cheap laughs from. Caveat emptor.
Poster from the original American theatrical release.