Blood-soaked and candlelit, Michael Mohan's "Immaculate" disabuses the notion that any conception is ever without sin. Starring Sydney Sweeney (who also produced the film), this cheeky, freaky, lushly designed horror movie presents as a giallo nunsploitation riff, but the script by Andrew Lobel is much more "Rosemary's Baby" than it is "The Devils."

Still, Mohan wants "Immaculate" to be an exploitation flick, and so it is an exploitation flick, which means he has adorned Lobel's script in texture, atmosphere and viscera, taking the genre seriously while also applying an ironic wit. He skews toward modern horror filmmaking, but has the references and deep film knowledge to make "Immaculate" feel more like a long-lost video nasty dredged up out of an obscure archive.

Sweeney stars as Sister Cecilia, a doe-eyed and docile devotee from Detroit who has traveled to Italy at the behest of a Father Tedeschi (Álvaro Morte) to take her vows at a secluded convent where she will care for elderly nuns.

Soon, shockingly, she's exhibiting pregnancy symptoms, her womb thrumming with a whooshing heartbeat under a sonogram machine. Her spontaneous conception is seen as a miracle, the resurrection of God. She has no choice but to carry this pregnancy to term, surrounded by senile nuns, controlling male leadership and a secret sect of the sisterhood who wear crimson shrouds over their faces.

It's something of a wonder to watch Sweeney as she undertakes Sister Cecilia's journey, transforming from a meek naif into something unexpected and wild, her pious discipline falling away with every indignity. As this swift, 89-minute film builds to an absolutely feral climax, we do believe her, perhaps most of all in the film's final, jaw-dropping moments, as she embodies a pure animal honesty.

Mohan directs the ever-loving hell out of Lobel's script, drenching every frame in color, light and shadow, sending cinematographer Elisha Christian's camera swooping around the characters, into coffins and down dark hallways.

There is an over-reliance on jump scares, which are only intermittently effective, because, as audience members, we're trained to expect them, and tire easily if they don't pay off. However, these fade to the background as the film evolves into more effectively suspenseful filmmaking as Mohan operationalizes darkness and light to intriguing ends.

It's goopy, gross fun, if not entirely terrifying. If there's a weak link, it's the screenplay, which toys with deeper social and sexual themes but skims along the surface and leaves loose ends unfinished. While it can be refreshing when a writer doesn't over-explain (or tie everything back to trauma), there are a few plot threads that could have been pulled taut for a more satisfying narrative.

Still, if some of the mysterious elements exist merely to add mood and tone, it's worth it. If certain aspects of the convent's culture go unexplored, it's because Sister Cecilia hasn't figured it out. This strange cult is as mysterious to us as it is to her, as it would be in any good folk horror film.

All these references include, but are not limited to: giallo, Hammer horror, Frankenstein, "The Omen," "The Wicker Man" (and even a shade of "Texas Chainsaw Massacre"). Ultimately, they coalesce during the bravura climax, which flips the script on "Rosemary's Baby," allowing for a kind of inevitable agency that finally drags "Immaculate" into a truly modern conception.

In that moment, any and all qualms fall away as the only appropriate reaction can be: "bravo."

'Immaculate'

3 stars out of 4

Rated: R for strong and bloody violent content, grisly images, nudity and some language.

Where: In theaters Friday. In English and Italian with English subtitles.