God help me, but I found the climax to “Insidious: The Last Key” to be quite moving.

For a horror sequel, anyway. Sequel-prequel in this case.

Sure, much of what’s come before that, an hour and 40ish minutes of backstory, lulling detail, inane banter and scenes one can only describe as “filler” interrupted by quick-cut soundtrack-amplified SHOCKS, is a bore.

And so much of what Blumhouse Pictures and screenwriter Leigh Whannell are concerned with these days is working each new film (this is  the fourth) into “The Insidious Universe.” Then there’s the job of giving Whannell, a sometime actor who found his true calling with “Saw,” another acting role where he gets to be the nerdy ghostbuster awkwardly creeping on starlets half his age (he’s about to turn 40).

With these other agendas to fret over, is it any wonder these movies have devolved from a clever “Poltergeist” variation into a weary, idea-starved formula was a supporting cast that’s aged past “cute” that can’t find a new fright to save its life?

A prologue shows us the abusive, working class childhood of our ghost-whisperer, Elise (Lin Shaye). Young Elise (Ava Volker) could see and hear the spirits in the Five Keys, New Mexico house she and her fearful brother Christian (Pierce Pope) grew up in. Her mother (Tessa Ferrer) understood. But her brute of a prison-guard dad (Josh Stewart) didn’t like hearing Elise’s vivid descriptions of executions at the prison, which she hadn’t witnessed.

“And his last words were, ‘Go ta HELL.”

Dad beat Elise with a cane. And those spirits in the house? They murdered her mom.

Fifty-seven years later, Elise gets a call from the new owner of the same house. No, she can’t go back there to dislodge the ghosts. She can’t. OK, she will, because otherwise, we have no movie.

She’ll bring along those ghostbusting pals who helped set up Spectral Sightings with her, Specs (Whannell) and Tucker (Angus Sampson).

“She’s psychic, we’re the sidekicks!”

They’ll get to the bottom of why this house is haunted and Elise’s lingering guilt over the brother (Bruce Davison plays Christian as an adult) she left behind. Yes, there’s a key, a door to unlock and an emergency whistle a mother has given to her child to recover.

Horror matriarch Lin Shaye, who owes her career to being the sister to New Line Cinema founder Robert Shaye, is a comforting presence at the center of these movies. But in the original films, she was the cavalry, riding to the rescue of whoever was desperate to rid themselves of supernatural problems, a supporting player who only had to make a strong impression in a few scenes. She’s no Helen Mirren and making her carry these movies is a burden she’s not up to.

Park her in a scene with horror vet (“Willard”) Bruce Davison, an accomplished character actor, and he underplays her/charisma’s her right off the screen.

The sidekicks have shown us their entire bag of character and acting tricks. They’re not as brave as Elise, and if she doesn’t make them wear white shirts and ties, they don’t register at all. The novelty’s gone and they’re not cute any more.  Giving them a ghost-busting RV (“The Winnebaghost”) doesn’t help.

The ghosts are the long-fingered ghouls with skeletal faces so popular in the genre these days.

All of which adds up to a movie that has no right to the touching finale Whannell cooks up, a nice payoff to a movie that isn’t really worth sitting through to reach that payoff.

MPAA Rating: PG-13 for disturbing thematic content, violence and terror, and brief strong language

Cast: Lin Shaye, Bruce Davison, Leigh Whannell, Spencer Locke, Angus Sampson

Credits: Directed by Adam Robitel, script by Leigh Whannell. A Universal/Blumhouse release.

Running time: 1:43