Production designer Meghan C. Rogers cooks up a fine M.C. Escher nightmare world of doors, dead ends and perils folding in on themselves for the drawn-out finale of “Imaginary,” another variation on the sinister side of having a childhood “imaginary friend.”

Unfortunately, most everything that precedes that overlong, climax-to-anti-climax and onward ending is just as “drawn out.” This Jeff Wadlow (“Truth or Dare,””Fantasy Island”) thriller grabs a simple concept and overthinks it into a dumb and rather dull 90 minutes surrounding maybe a dozen minutes of delivering chills.

But mixed in with all the metaphysical mumbo-jumbo of “explaining” what might be going on — much of it coming out of the mouth of Broadway legend Betty Buckley — at least we learn a new word. “Parocosm,” that’s what the broader idea of imaginary worlds, often created in childhood, is called.

DeWanda Wise of “The Harder They Fall” and “Jurassic World Dominion” stars as Jessica, a children’s book author and illustrator happy to escape the nightmares of a city apartment and move, with her new musician husband (Tom Payne) and his teen (Taegen Burns) and pre-school (Pyper Braun) daughters back to the house she grew up in somewhere in Louisiana.

Her books are about Molly the Millepede and her struggles with Simon the Spider, mild-mannered scary material aimed at the very young. Might they somehow tie into her past and that prologue that saw a Black family struggling with something demonic hidden behind a crawl-space door?

When little Alice, “Ally” (Braun) finds Chauncey, an old Teddy bear tucked away in Jessica’s old house, we start to get our answers.

Chauncey talks to her, or rather we hear her voice his side of conversations that involve games, tea parties and a scavenger hunt.

Jess overhears this chatter and is charmed and amused by it. Some of it even inspires her next story about that millipede, a real help to an illustrator with a deadline. And it’s a welcome break from the drama of the rebellious teen whose criticism of her various “step-mom” moves is not a help.

Ally, we’ve noticed, has a scar. Her birth mommy is “sick,” which must have ended the marriage. Jess has a scar, too.

And the violence of both their pasts informs what is to come as whatever Chauncey is, childhood “friend” doesn’t seem the best description.

The performances are mostly competently indifferent, although young Miss Braun packs a punch as a mouthy child who isn’t shy about asserting herself to an imaginary friend who seems bent on causing her harm.

The narrative steps on familiar touchstones of the genre — “irresponsible” fifteen year-old not taking care of her sister because there’s a cute teen boy next door, Chauncey “testing” Ally and making Jess anxious, the tuned-out husband who has to go “back on the road,” and the “chatterbox” neighbor (Buckley) who seems to know all about Jess’s past and what might be going on with Ally.

“People don’t believe in otherworldly things, until they have to.”

None of it’s handled with much pace, humor, suspense or style until our third act journey into the NeverEver. And even that, derivative as it is, misses the mark in terms of real frights.

“Explaining” is almost always over-explaining in horror, because the best jolts come from the shock of the unknown and unknowable. The “Imaginary” is always lot spookier than the “explained.”

Rating: PG-13, violence, suggestions of teen drug and alcohol abuse, profanity

Cast: DeWanda Wise, Pyper Braun, Taegen Burns, Tom Payne and Betty Buckley.

Credits: Directed by Jeff Wadlow, scripted by Greg Erb, Jason Oremland and Jeff Wadlow, A Lionsgate release.

Running time: 1:44