Taking the notion of skeletons in the family closet quite literally, Alex Winter‘s Adulthood sets out to expose something sinister lurking just beneath suburbia’s fake wood-paneled veneer of respectability. In the case of adult siblings, Megan and Noah, it’s the discovery of a seriously decomposed cadaver stuffed behind one of the basement walls of their childhood home that forces them to reassess their seemingly conventional upbringing.

It’s certainly a tasty premise — one that holds considerable noir-tinged promise — and for at least the first half of the film, the quirky blend of increasingly grisly goings-on and wryly observed social commentary forms a cohesive whole before veering irretrievably out of sync.

While Kaya Scodelario, Josh Gad and a cast of colorful characters keep it all reasonably engaging, the film, which was handed its world premiere at TIFF and is scheduled to arrive in select theaters Sept. 19 ahead of a streaming bow four days later, falls short of reaching its full potential.

Reuniting at their small-town family homestead when their invalid mom has been further incapacitated by a stroke, methodical Megan (Scodelario) and her melodramatic brother Noah (Gad) are reliving childhood memories in their musty basement when they make that fateful discovery behind some damp drywall. It doesn’t take long for them to make the connection that the rotting corpse is that of their next-door neighbor, Mrs. Metzger, who had gone missing back in the ’90s.

Whispers at the time implicated her since-deceased husband as the culprit, but this recent development has Megan and Noah putting their mom and late dad on top of the list of likely suspects. Afraid to call the cops at the risk of losing their inheritance to a crime scene, Noah, an out-of-work L.A. screenwriter, contends he knows what’s best after having worked two seasons on Blue Bloods: They’ll bury Mrs. Metzger’s body in the swamp.

Alas, she doesn’t stay submerged very long, and in short order the police pop up at the hospital where their recovering mother is still unable to speak. Meanwhile, her plotting caregiver (Billie Lourd) shows up at the house claiming Mom admitted to killing Mrs. Metzger and she will take that information to the authorities unless she’s paid $10,000.

Now in full panic mode, Noah calls in back-up in the guise of their weird cousin Bodie (a terrific Anthony Carrigan), who’s something of an Uncle Fester-Freddy Krueger mash-up with a scary weapons collection. But the more he and Meg try to dig themselves out of the nightmare, the deeper they get pulled in, with a mounting body count to match.

In his director’s statement, Winter, whose more recent behind-the-camera output includes documentaries profiling Frank Zappa, YouTube and showbiz kids, counts Alfred Hitchcock, Dashiell Hammett and Bong Joon-ho as key influences in his artistic vision for the script by Michael M.B. Galvin (Fat Kid Rules the World.). That may have been Winter’s intention — there’s also more than a whiff of the Coen brothers figuring into all the mordant mayhem — but the execution proves trickier to pull off for a sustained period. While Winter maintains an effective grip on the desired “noir-lite” tone early on in the proceedings, as Megan and Noah’s lives begin spiraling helplessly out of control unfortunately so does that crucial dark/light balance. By the time Megan seizes control of the reins at the film’s close, the abrupt denouement feels jarringly disconnected rather than organic to the storytelling.

Winter’s cast is certainly up to the seriocomic challenge, with Gad playing a pitch-perfect man-child in an Alamo Drafthouse t-shirt who can’t help but notice that his life has turned into one of his unsold scripts. Meanwhile, Scodelario (Teresa in the Maze Runner film series) is convincing as a wife and mother already contending with a high-stress job and a diabetic child, who comes to rationalize that the apple might not fall far from the tree where her larcenous mama is concerned.

The production also takes good visual advantage of its many scenic Ontario, Canada, locations, especially a sweeping pivotal sequence that’s shot on the SkyBridge, which holds the record as the longest pedestrian bridge in North America.

If only Adulthood could have ended up making it to the other side.