Everyone knows what PTSD means, but Diederik Van Rooijen’s horror movie introduces us to something new—an affliction that might be termed PEPS, or post- exorcism possession syndrome. On the evidence of “The Possession of Hannah Grace,” however, it’s not a condition one is likely to encounter in a theatre more than once.

That isn’t because the movie is an awful example of the genre; in fact, it’s better-made than most, and manages to achieve a generalized creepiness, as well as a few genuine shocks. Ultimately, however, it becomes repetitive, unable to sustain the premise even for its brief 85-minute running-time.

The exorcism part of the plot occurs in a relatively brief prologue, where we see Hannah (Kirby Johnson) possessed by a demon that two priests are trying to expel as she lies writhing tied to a bed, issuing threats between prayers and sprinkles of holy water. When the demon proves too powerful for the clergymen, whom it telekinetically seizes, raises in the air and begins to crush to death, her distraught father smothers Hannah to death.

But, of course, he’s not taken PEPS into account.

Months later, Megan (Shay Mitchell), a young woman whose career as a police officer was shattered with the death of her partner and is now a recovering addict, has gotten a job as the night morgue attendant at a Boston hospital thanks to her sponsor Lisa (Stana Katic), a nurse there.

On her very first shift, however, something very odd happens. One of the corpses delivered is that of a badly disfigured young woman, whom she identifies as Hannah Grace, a girl her investigation indicates died in a botched exorcism some time ago. Strange noises and shadowy movements begin to occur. Even odder, the corpse shows signs of changing, its injuries gradually diminishing.

It turns out that the changes are the result of activities that the reanimating corpse undertakes when out of Megan’s sight. These involve encounters with other members of the staff, including Lisa and goofy security guard Dave (Max McNamara). What’s happening will be explained by a mysterious intruder (Louis Herthum) who sneaks into the morgue with a definite mission in mind. There will be other visitors as well—Dave’s lethargic partner Ernie (Jacob Ming-Trent); Andrew (Grey Damon), a cop who’s also Megan’s ex-boyfriend; and Randy (Nick Thune), a philosophical ambulance driver. Most meet an unhappy fate.

It doesn’t take very long for the script to reveal its rather simple secrets, and the scenes of Hannah attacking her victims don’t show sufficient variety. But the production design by Paula Loos is eerie, and cinematographer Lennert Hillege uses light and shade skillfully; the effects—except for those involving the crematorium—are good as well (especially those showing the look of Hannah’s corpse and its spidery walk, nicely executed by Johnson and edited by Stanley Kolk and Jake York). John Frizzell’s score is nicely understated, with the “gotcha” moments avoiding the sudden blare of noise that’s almost obligatory nowadays. Most importantly, Van Rooijen, making his English-language debut, shows that he can create a spooky atmosphere while not drenching everything in gore.

As to the performances, Mitchell is merely adequate as the heroine, and the rest of the cast is simply okay, though McNamara offers a bit of Michael Pollard weirdness and Thune is nicely laid-back.

“The Possession of Hannah Grace” gets about as much mileage out of its thin premise as could be expected, and exhibits some cool visuals along the way; but that’s not quite enough.