The exact moment The Book of Henry lost me was when Naomi Watts reached for the ukulele. About 20 minutes into Colin Trevorrow’s new film, as Watts’s single mom character Susan tucks her kids Henry (Jaeden Lieberher) and Peter (Jacob Tremblay) into bed, she performs a cheerful goodnight song that pushes things into twee overdrive. The first half of The Book of Henry is a strange, saccharine family story, crammed to the gills with forced quirkiness, following the savant-level genius child Henry as he runs his household at the age of 11.

Henry bankrolls the family with stock-market earnings, tuts at his mother as she plays video games late into the night or goes out drinking with her lush of a co-worker (Sarah Silverman), and entertains his little brother in a steampunk treehouse filled with various Rube Goldberg contraptions. His only real struggle is that he can’t exert similar control over the darker side of human nature—specifically, why he can’t stop his neighbor Glenn (Dean Norris), the town’s police commissioner, from abusing his stepdaughter Christina (Maddie Ziegler). So Henry starts to formulate a plan. And that’s when The Book of Henry goes from being just plain bad to deeply, deeply weird.

When Trevorrow decided to make this film, based on a script by the crime novelist Gregg Hurwitz that was written almost 20 years ago, he had just overseen the massive success of Jurassic World, a boringly competent but wildly successful revival of the dinosaur franchise. He could have made anything, and he chose a small-budgeted family drama, the kind of film Hollywood makes less and less of. But it’s hard to know what possibly could have drawn him to this script, a bizarre mash-up of a quirky comedy, a weepy drama, and a hard-boiled thriller that ends up feeling like a mutant Lifetime movie with an ending straight out of a fever dream.

It’s hard to describe what happens in The Book of Henry without spoiling some of its twists, but if you’ve seen the film’s trailer you know that Susan ends up buying a high-powered rifle, and that Henry’s interest in Glenn’s crimes definitely extends into the realm of obsession. Put it this way: At one point in the movie, Susan exasperatedly shouts at her son, “We are not killing the police commissioner, and that’s final!” as if she’s putting her foot down about a second portion of ice cream. There’s a fundamental tonal miscalculation at the heart of this film that’s further exposed as it goes on. The Book of Henry tries to be a movie about the perfect murder and one about a fun, unconventional family simultaneously, and the harder it tries, the more unhinged it seems.

The mixing of family schlock with a revenge thriller is the kind of high-wire act that even a great director would struggle with—Trevorrow, unsurprisingly, falls face-first in his attempt, accidentally crushing some of the onlookers below. But the warning signs are there from the beginning, from the moment Susan pulls out that ukulele. There are so many alarming misjudgments; every line reading set my teeth on edge, every example of Henry’s supposed grown-up genius made me squirm. His relationship with his mother, who he bosses around like an exasperated husband, is borderline upsetting, but his fascination with Christina is perhaps even stranger.

This is a film about child abuse—there’s no ambiguity about Glenn’s guilt, although the PG-13 rating means the specifics of what he’s doing are left to the imagination—but it’s abuse that’s entirely glimpsed through Henry’s bedroom window. Trevorrow and Hurwitz make no effort to turn Christina into anything more than a prop, a silent plot driver for the demented twists and turns the movie takes, whose glum face and monosyllabic responses to questions are all the characterization she’s allowed. Near the end of the film, Trevorrow tries to rectify this oversight by giving Christina a showcase moment out of nowhere as a grand, emotional climax. But by then, it was far too late—my theater audience was howling with horrified laughter.

So-bad-they’re-good cult classics like The Room or Battlefield Earth are always best when they’re made with sincere intent; there has to be a particularly odd, alien quality to their storytelling, something that’s not that far removed from Hollywood formula, but that uses all the wrong ingredients. The Book of Henry is the equivalent of eating a cake baked with salt instead of sugar, or listening to a Beatles song where the lyrics are in Esperanto—you understand the idea of what Trevorrow was going for, but the end result is an appalling, irradiated mess, a Frankenstein’s monster version of a feel-good classic. It might be quickly forgotten as a well-meaning flop, but The Book of Henry deserves to linger—it’s like an unsettling dream you can’t quite remember, a familiar story where all the pieces just seemed out of place.