From the outset, there’s every reason to think The Book of Henry will be good.

The foremost driving force behind such robust optimism is it being Safety Not Guaranteed director Colin Trevorrow’s return to small movies between Jurassic World and Star Wars installments.

A likable cast further boosts the film’s potential and for a while it’s a jolly precocious youth tale centering on the titular 11-year-old genius (Jaeden Lieberher, Midnight Special) being the dependable force for his younger brother Peter (Jacob Tremblay, Room) and quasi arrested development mom Susan (Naomi Watts) in rural New York.

Among Henry’s numerous quirks are trading stocks on the schoolyard payphone, inventing Rube Goldberg machines in his treehouse workshop and sketching T.S. Spivet-like observations of his world. But despite the firm foundation of good-natured chuckles at this preteen’s remarkable accomplishments and general cheerful attitude, the film soon starts to feel like Trevorrow's favor to novelist Gregg Hurwitz, noticeably making his feature screenwriting debut.

Warning signs appear toward the end of the first act when Henry bursts into the office of his school’s principal (Tonya Pinkins) and tears into her about not following up on his classmate/neighbor Christina (Maddie Ziegler) wearing the signs of abuse at the hands of her stepfather Glenn (Dean Norris, typecast once more), who just so happens to be a high-ranking local police officer.

Though Henry’s words suggest otherwise, his unseen monitoring of the situation and the lack of convincing evidence that Christina is in trouble (e.g. no bruises, contrary to Henry’s claims) make the accusation feel random. And while Glenn’s actions don’t need to be shown, with so much left to viewer imagination concerning the matter as the film progresses, watching Henry and others get worked up about Christina is almost like watching an entirely different movie.

Hurwitz soon drops this thread when Henry develops health issues, a stretch that allows the boy’s idiosyncrasies (and in turn the film overall) to shine once more, later looping it back in with an unusual turn that seems like a way for Susan and Peter to cope with Henry’s illness but quickly turns ludicrous and sentimental, unraveling the characters’ appeal.

Gifted as Henry is, nothing in the film suggests that he could record an instructional tape for Susan to guide her through his proposed plan in real time, full of perfectly placed retorts to her knee-jerk responses to his orders. Susan may be predictable, but not to that implausible extent.

Nearly as difficult to swallow is the series of silly encounters Henry’s call to duty inspires, all of which are unfitting of the characters who step out of their comfort zones. Here and elsewhere in The Book of Henry, one can see the points Hurwitz is trying to make, and while they’re noble in theory, they’re underdeveloped and borderline offensive in their simplicity.

So it goes for Susan’s desire for normalcy in working at a local diner — where she keeps her healthy bank account a secret from her immature co-worker Sheila (Sarah Silverman) and boss John (Bobby Moynihan) — and the weak ass yet obvious inferences that Henry’s doctor (Lee Pace) is going to wind up dating if not married to Susan.

There’s a lot to these relationships and others in The Book of Henry, but as interpreted by Trevorrow and Hurwitz, only scattered portions of them are worth telling. It’s therefore only fitting that merely a fraction of the film is worth watching.

Grade: C-plus. Rated PG-13. Now playing at Carolina Cinemark

(Photo: Focus Features)