“M3GAN” is a fierce and fun thriller about a doll that develops a murderous mind of its own. Sure, that’s as tired a trope as there is in the horror realm. But this laugh-out-loud dark comedy flirts with being THE murderous doll movie.

With a brilliant melding of child-in-a-suit and CGI, hints of satire and grim, knowing laughs about tech addiction and the death of human connection, this pretty good film could have been great.

A little girl (Violet McGraw) loses her parents in a car accident and is sent to live with her toy company robotics whiz Aunt Jemma, played by Allison Williams.

Thirtysomething Jemma isn’t exactly “mother” material. She has toys, but they’re “collectibles.” She doesn’t have a job, she has an all-consuming career. When it comes to responding with compassion and empathy to a child who’s just lost her parents, Jemma can’t even seem to manage the human touch, much less a hug.

And it’s not like she’s weeping herself at the loss of her sister and brother-in-law. Talk about “robotic.”

Jemma’s real passion is a robot doll she and her team (Jan Van Epps and Brian Jordan Alvarez) have been secretly prepping for their robotics play-pal toy company. She’s even hidden “M.3.G.A.N.,” the “Model Three Generative Android,” from their deadline-obsessed/cost-conscious boss (Ronny Chieng, damned funny) who dismisses the prototype as a “cyborg puppet show” — at first.

But Jemma is hellbent on swinging for the fences, and realizes that the doll can be programmed to do a lot of things she’s too far down the Sheldon Cooper spectrum to manage — childcare, child instruction, and simply listening and paying attention.

A demonstration lets M3GAN show off her ability to learn from nine-year-old Cady, pick up on her unhappiness and both comfort her in her grief and distract her from her lonely, loveless misery.

But as the two are “paired,” Jemma’s level of control slips. And as we’ve heard “keep Cady from harm” is M3GAN’s prime directive, we can see what’s coming, even if clueless Jemma cannot.

In the later acts, the doll takes on standard double-jointed monster motion straight out of “The Ring” and scores of skittered, body-contorting menace imitations — really over-the-top stuff. But the best effects might be the simplest — a plastic-faced doll with human-eye shaped cameras silently following Cady and potential threats around her, judging and perhaps plotting.

The doll’s design might seem to be guided by the young actress cast to “play” her, Amie Donald. But to me she looks like Chloe Grace Moretz did when she first started turning up in films. And that’s just...creepy. Moretz could seem a little scary in her tweens. And she might have a good name-image-likeness licensing case, if she were to pursue one.

The movie’s jokes are fangirl and fanboy-friendly jabs at pop culture, tech-obsession and people’s shock at “meeting” this “toy” for the first time.

The frights are mostly jolts that come from the viewer realizing this or that deadly thing the doll can do and how it’s “learning” to do even more.

Director Gerard Johnstone (“Housebound”) and the Blumhouse team take their time setting up this story, with a preamble TV commercial about the state of interactive toys at the beginning of our tale, before the great M.3.G.A.N. leap forward, and the snowy accident that kills Cady’s parents. The startling stuff that follows is played for dark laughs.

And the finale is full on gonzo.

But there’s a dead-zone in the midst of all this fun, and it comes from the soulless automaton who’s supposed to be raising Cady. At first, I thought it was just an acting choice by our Jemma. But her blank-faced under-reactions to the perils that blow up in that third act had me wracking my brain for where I’d seen this pretty but bland actress before.

I didn’t immediately recognize “Get Out” villain and “Nepo Baby” poster child Allison Williams as the player who was letting down the side here. There’s no mincing words, young Ms. McGraw gives the movie a little pathos, and the damned plastic doll acts rings around Williams.

There are a couple of plot twist choices that keep this generally entertaining thriller from transcending genre and becoming something special. But there’s a also casting choice that mutes our emotional connection to the story and seriously waters-down how alarmed we’re supposed to be when things turn truly alarming.

It’s one thing to overplay the whole “can’t really warm up to a grieving child” thing. But the rule is, the audience can’t get scared if the actors playing the potential victims can’t convince us that they are. Williams doesn’t.

With its laughs and harrowing violence, “M3GHAN” plays, which is all you can ask of any movie. But a brilliant start, great effects and a blend of cleverness, pathos and satiric awareness of the world it premieres it suggest that it could have been much more.

Rating: PG-13 for violent content and terror, some strong language and a suggestive reference

Cast: Allison Williams, Violet McGraw, Amie Donald and the voice of Jenna Davis

Credits: Directed by Gerard Johnstone, scripted by Akela Cooper. A Blumhouse/Atomic Monster production, a Universal release.

Running time: 1:40