You see as many horror movies as I do, you start to obsess on the one or two things the ones that work get right.

A pet peeve? Actors who, because they’re not good at interacting with effects or can’t find in their imaginations the proper degree of shock and awe that someone experiencing the supernatural would register.

Lee Pace (“Guardians of the Galaxy”) and Carrie Coon (“Gone Girl”) put on a clinic as to how it’s supposed to play in “The Keeping Hours.” Parents, gutted and eventually broken up by the death of their little boy, are brought together by the impossible. The kid’s still in their old house.

Screenwriter Rebecca Sonnenshine and director Karen Moncrief conjure up sentimental and sad ghost story about loss, guilt and “unfinished business” that manages to be genuinely touching. Cast your horror movie well and that sort of thing is possible.

Not that they don’t have some frights to share. Here’s my favorite. Bitter, ill-tempered Mark has just started cleaning up the house he and his ex split from years before, when their five year old Jacob (Sander Thomas) died. The latest renters have fled and there’s all this stuff Mark and his ex, Elizabeth, left stored in the attic.

That’s where Jacob used to play. And Mark, irked, calls her voice mail to get Elizabeth over there to pick up anything she wants because “I’m finally selling.”

The word “selling” is barely out of his mouth when every single door in the hallway he’s calling from — five of them we can see — SLAMS shut. Chilling.

The best effects are the simplest, and kudos to the effects rigger or production assistants who nailed this precision-slamming in one take. We, like Lee Pace playing Mark, his mouth agape, are shocked and shaken that something inexplicable has just happened.

The radio starts playing “The First Time Ever I Saw Your Face,” which Jacob heard as “best man” at his parents’ wedding. And in the attic, Mark sees the boy. Another shock. How can this be?

He tracks down the dog walker (Ana Ortiz, a hoot) who had been “consulting” with the previous tenants, because, you know, her MAIN job is “medium.”

“You SAW him? You didn’t conjure him, did you? You have a brain tumor or some other medical condition? Family history of mental illness?”

My father has dementia.

“Technically, that’s a cognitive disorder and not a mental illness. What did he WANT?”

He wants his mother.

Janice’s advice? Do what the kid asks. And because in LA, you never underestimate the dog walker, that’s what Mark does.

Elizabeth’s reaction when she sees a little boy in Jacob’s clothes and play mask? Fury. She gives Mark a bloody nose, suggests he seek help, sure he’s played a sick joke.

But eventually she relents, returns and is amazed.

The film begins with their wedding day, and then jumps ahead to the fictive present. Mark, brusque with everyone, including the lady next door (Amy Smart) and her pesky son, establishes much of what happened through visits with his father, the one with dementia. He’s seen Elizabeth on TV. “She’s written a book.” It’s about moving on from grief, and no, they’re not still married. Six years divorced, Jacob dead for seven.

Ray Baker, by the way, plays a beautiful and compassionate take on dementia.

Pace lets us see Mark lose little pieces of his sanity and regain the compassion we fear he lost with his kid. Coon brings a fine “Not having this” to her first moments with her ex, the old “I remember why we split up, even if you don’t” routine.

“I thought you dropped drinking.”

“I did. Mostly.”

I like the way the script sets up the requisite “rules” that those interacting with the supernatural world follow, and just love Ortiz’s version of the “Been there, seen it” “medium” Janice. It’s a worn movie trope that such folks, from “Annabelle” to “The Conjuring,” on back to “Poltergeist” — must be unflappable, direct and a bit funny. Ortiz, of TV’s “Ugly Betty,” nails it.

“Keeping Hours” doesn’t play up its handful of frights. The filmmakers are more interested in what this experience means to the long-divorced people living through it. That robs the picture of surprise and the “gotcha” moments common to this genre these days.

But not every ghost in the movies has to be a demon, not every ghost story has to be an assault.

And sentimental as the picture is, it starts slowly and only finds its heart in the third act.

I still say “The Keeping Hours” is a keeper.

MPAA Rating:PG-13 for thematic elements, some sensuality and language

Cast: Carrie Coon, Lee Pace, Amy Smart

Credits:Directed by Karen Moncrieff, script by Rebecca Sonnenshine. A Universal/BH release.

Running time: 1:31