That’s how director Michael Mohan approaches “Immaculate,” his horror movie with the suddenly ubiquitous Sydney Sweeney at its center. Written by Andrew Lobel, it has a little bit of everything on the horror front: body horror, Catholic horror, the notion of what sin is and where it fits in the world, questions of faith and belief and miracles and what happens when a believer is confronted with things that throw the accepted order of things out of whack.

It’s OK, but while those ideas exist in the film, they’re not explored in real depth once it takes a turn in the third act and gets busy with the grisly work of trying to make you hide your eyes or groan in disgust. The shift isn’t just in tone, it’s in story. Genre, even. Which is fine — the last part of the movie is the most exciting. But it’s a jarring shift, and the bigger ideas get left behind.

What is 'Immaculate' the movie about?

Sweeney, who is quite good, particularly when she adds a little world-weary humor to an increasingly desperate situation, plays Cecilia, a devout young woman from Michigan who survived a near-drowning as a girl and has been convinced God saved her for a reason ever since.

Time out for what may sound like faint praise but isn’t, because it’s an important part of the performance: Sweeney unleashes one of the most harrowing screams I’ve ever heard in a movie, and I’ve watched a lot of horror films. It’s truly impressive, like Roger Daltrey at the end of “Won’t Get Fooled Again,” only blood-curdling.

Cecilia goes all in on her devotion, joining an Italian convent (while trying to learn Italian), arriving just in time to take her vows and become Sister Cecilia. It’s a creepy place, and not only because it serves mostly as a hospice for older nuns before they die. A prologue warns us before the film even starts that it isn’t exactly a hotel you can check in and out of.

Cecilia strikes up a friendship with Sister Mary (Simona Tabasco), an independent spirit who joined the convent to get away from an abusive relationship and bristles under the harsh order of the place. She welcomes Cecilia’s presence; everyone else seems either put off by her or excessively reverent.

Soon Cecilia starts having nightmares and has weird experiences with some of the nuns.

And then she learns that she is pregnant.

Sydney Sweeney goes from a whisper to a scream

She has never had sex, she swears and the convent doctor confirms. This, she is told, is why God spared her — for immaculate conception.

That’s when things get really weird. Cecilia, not surprisingly, is somewhat skeptical about the whole thing, though she clearly is pregnant. Sister Mary is even more so, and more vocal about her doubts. (Tabasco is a welcome splash of cold water in the face in her infrequent appearances, livening things up.) Father Tedeschi (Álvaro Morte) assures Cecilia that she is indeed the miracle they have been praying for, and maybe she is. But there’s a lot more to it than that.