“Bones and All,” the new film from Luca Guadagnino, director of “Call Me by Your Name,” promises a plenteous serving of blood and guts. Yet this coming-of-age story of a teenage cannibal is not exactly the generic horror flick the trailers and commercials lead one to expect. 

Played by Taylor Russell of the “Escape Room” franchise, Maren has shown an appetite for human flesh apparently from an early age. Her father, Frank (André Holland), locks her door from the outside before bed, but that does little to deter her from sneaking out one night for a sleepover at a classmate’s home. She of course lapses, forcing father and daughter to evacuate their home before cops arrive. Fed up with this routine, Frank abandons Maren, leaving behind a Walkman containing a voice message, an envelope of cash, and her birth certificate. Having received the name and address of her long-absent mother, Maren spends the money on a Greyhound ticket. 

During the course of her journey, encompassing half a dozen states, Maren encounters many others who share the same predilection. They call themselves “eaters,” and apparently possess a heightened sense of smell that enables them to identify one another from a distance. They seem to reconcile with the amorality of cannibalism by establishing their own rule of thumb on what they consider to be the most ethical way to satiate their hunger. 

Sully (Mark Rylance), a creepy old man who offers to show Maren the ropes, will only feed on the dead. Lee (Timothée Chalamet), on the other hand, targets those whom he deems to be unsavory characters. Although seemingly wary of others of his kind, Lee offers Maren a lift in a pickup truck taken from one of his victims. 

Screenwriter David Kajganich, who previously collaborated with Mr. Guadagnino on 2015’s “A Bigger Splash” and 2018’s “Suspiria,” adapts from Camille DeAngelis’s 2015 young adult novel. The author, who is vegan, has noted that she means for her work to be an allegory on carnism, which Mr. Kajganich alludes to in a scene with Maren and Lee taking refuge in a cattle barn. Yet that’s beside the point of either the novel or the film. 

While the basic premise is unchanged, the film contains so many altered details that it no longer conveys the same message as the book. Most notably, Mr. Kajganich has arbitrarily swapped the genders of several characters. The source novel admittedly has its shortcomings, but it explicitly concerns Maren’s self-discovery of what triggers her cannibalistic instincts and ergo dooms her to a life of loneliness. Her targets all fit a certain profile in the book, which is not at all the case here. Although the ultimate outcome doesn’t differ, Ms. DeAngelis’s intended message is lost in the adaptation. 

At the novel’s conclusion, Maren arrives at a place of inner peace and self-acceptance, but Mr. Kajganich has framed her more as potential prey than as a predator, stripping away much of her agency. In the absence of some of Ms. DeAngelis’s most original ideas, the film comes off like some derivative of “Let the Right One In” and “Interview With the Vampire.” While its horror markers are few and far between, the film is much more graphic than the source material, which is descriptive about everything but the gory details.  

Mr. Guadagnino filmed on location in four different states. Like Wim Wenders and other European filmmakers making road movies set in the U.S., Mr. Guadagnino paints Americana with the broadest of strokes. One can hardly discern the specifics of the locales without superimposed titles on the screen. The score by Trent Reznor and Atticus Ross is likewise nondescript. 

The film engrosses for the most part, eliciting empathy for a monster — just as the novel does. Ms. Russell and Mr. Chalamet draw out the humanity of their morally reprehensible characters, and Mr. Rylance is both folksy and menacing. The third act drags a bit, making viewers wonder just exactly where everything is headed. By the time the film reaches its predetermined destination, the entire journey has lost its meaning. Cannibalism as a central metaphor has also become quite gratuitous.