PHOTO BY BRUNO CALVO / WARNER BROS.

When there are no rules to your story, I suppose, you can keep it going for as long as you want.

Across the two chapters of “The Nun,” there’s no consistency to how the titular habitual demon operates. Sometimes it’s a walking, glowering nun. Sometimes it possesses the nearest human. Sometimes it’s invisible. Sometimes (not often enough, frankly) it’s some kind of wolf creature. Sometimes it can be stopped with a quick prayer, other times it’s an unstoppable force.

They’re just trying to get from one jump scare to another, after all. Let’s not pretend they’re thinking about this story, so why should we?

In the original, an out-of-the-way Romanian abbey held a sinister secret: There was a revolving door to hell in the basement, and a nasty demon most often seen in the form of a sinister sister (Bonnie Ahrens) had escaped. Irene, a novitiate (Taissa Farmiga), had to accompany a priest (Demian Bichir) to defeat the beast with the help of a vial of Jesus’ blood.

A few years later, the priest has died offscreen — largely because Bichir has better things to do — but the demon is back. Irene will head off with the help of a young associate (Storm Reid) to try to overcome evil once again, in the form of a potentially possessed side character from the original film (Jonas Bloquet).

The strongest aspect of the original film was a spooky and interesting setting, and the sequel fails to replicate it; a dusty old boarding school in France doesn’t create the right atmosphere. “The Nun II” is thereby left to live and die — almost exclusively the latter — on its scares and shocks, which are predictable and toothless.

Farmiga is the sole standout, having grown considerably in the role; she seemed overmatched in the original but projects something close to grace this time around. It’s not enough, but it’s good to see her develop as a performer.

And hey: That wolf creature is pretty good. Extra point for the wolf creature.

My Rating: 4/10

“The Nun II” is now playing in theaters.