A prologue introduces an unnamed figure crouching over a body, tearing flesh from a shoulder, driven by an insatiable compulsion the novel capitalizes as "Hunger." A framing letter from Cecil H. Smith, PhD, founder of Monstera BioSciences, addresses the FDA's refusal to approve a weight loss drug called Obexity (generic name ephaloma-copiramate, or EmaC-8). Smith argues the drug can "eradicate obesity forever" and dismisses concerns about a trial participant who developed "an acquired taste for human flesh." An investigation identifies the participant as Emmett Truesdale. His blog posts, health journals, and Instagram account form the novel's mixed-media structure.
Emmett is a 28-year-old gay man in San Diego, working at Target and weighing above 310 pounds. His life is defined by stagnation and shame: no promotion in years, no boyfriend since college, an unused master's degree in education, and a constant fear of health catastrophe. He lives with his best friend, Lizette Castillo, a body-positivity advocate who runs an extended-size clothing brand called GORDITA and opposes Emmett's desire to lose weight, viewing it as internalized self-hatred.
When Emmett spots an Instagram ad for a weight loss clinical trial, the two attend an information session at Monstera's headquarters. Dr. Jenni Saito, the director of product development, presents Obexity as a two-part treatment: gene therapy that rewrites DNA related to energy conversion combined with regular injections of EmaC-8. Trial participants receive the treatment free and can lose weight rapidly without changing their habits. Emmett is captivated.
Blog posts and interview transcripts reveal his painful history. His stepfather, Hank Stauder, a PhD scientist, monitored Emmett's eating with escalating cruelty, calling him a "fat pig" and driving him to eat in secret. In the worst episode, when Emmett was 11 and his mother, Joanna, was away, Hank starved him for days, force-fed him until he vomited, tied him to gym equipment, and used a funnel to make him re-consume his own vomit. Joanna arrived home, found Emmett bound, and struck Hank with a dumbbell. The couple divorced, and Hank disappeared. An earlier blog post recounts a Christmas when 10-year-old Emmett bit Hank's hand during a struggle over food, tasting blood mixed with icing and finding he liked it.
Approved for the trial despite a type 2 diabetes diagnosis, Emmett undergoes the gene therapy procedure, which is harrowing: He remembers being conscious as surgeons extracted bone marrow, forced a feeding tube down his throat, and injected dark fluid into his belly, though a nurse insists these memories are anesthetic-induced nightmares. He tells Lizette nothing, afraid she will stop him.
After weeks of no results, he wakes one morning having lost six pounds overnight. The dramatic weight loss continues, averaging roughly a pound per day. His diabetes reverses, and he begins posting before-and-after photos on Instagram, where his following grows from under 100 to over 5,000. During a visit to the Museum of Us in Balboa Park, he encounters Aaron Wolfe, a former grad school crush now serving as the museum's education director, and they begin dating. The museum's "Savage Hunger" exhibition includes a portrait of Sir Percival Blount, a 17th-century baronet whose medicinal tonic allegedly left him craving human flesh.
Emmett earns a promotion at Target and interviews for an education manager position at the museum but loses the job to another candidate. Yet disturbing side effects emerge. He wakes with dried blood on his hands and no memory of the previous night. He learns that Georgina Hodge, a nonprofit director who once discriminated against him, has been found dead, her death attributed to a coyote attack. He experiences blackouts, and his cravings shift to raw meat, then to something he cannot name. News reports document a surge in aggressive coyote attacks across San Diego, beginning the same month the trial started.
He discovers in the Phase I trial report that a previous participant was imprisoned for murdering and eating her ex-husband while on the drug. He confronts Dr. Saito, who offers soothing explanations, implies she has taken Obexity herself, and frames the trial as essential for people like them. Persuaded, Emmett continues.
Aaron's education manager resigns, and Aaron offers Emmett the position. Shortly after, Emmett finds a bludgeoned corpse in his car trunk, realizes he killed and partially ate the man during a blackout, and burns the car to destroy the evidence. He confesses to Lizette, who is horrified but loyal and convinces him to destroy his remaining doses. Without EmaC-8, his weight rebounds rapidly, his relationship with Aaron deteriorates, and his museum colleagues grow distrustful. Desperate, he obtains black-market doses from Niño, his half-brother Chris's friend, and kills again, luring a former hookup named Justin Matthews to Justin's apartment.
Monstera offers Emmett a deal as the public face of Obexity: a national advertising campaign, generous compensation, and a lifetime supply of the drug. He accepts, knowing the drug turns people into killers but unable to face returning to his former body. The partnership announcement goes live on Instagram, revealing that his transformation came from a pharmaceutical rather than willpower. His followers erupt with outrage.
Aaron arrives at Emmett's apartment to fire him and calls him a "monster," triggering drug-induced rage. Emmett kills him. Dr. Saito calls, revealing she knows about all the murders. She explains that Assistant Police Chief Bautista, a Phase I participant, has been misdirecting investigations, and that Monstera genetically modified the coyotes plaguing San Diego to cover for Obexity-related deaths. She drives Emmett to the company founder's house and asks him to take the fall. En route, she confesses she deliberately preserved the drug's violent side effects, wanting Obexity to enable fat people's revenge against those who tormented them.
Alone in the house, Emmett discovers a chest press identical to the one Hank tied him to, a print of the Blount portrait from the museum, and a Book of Mormon inscribed to "Hank" with the name "C. Henry Stauder." Cecil H. Smith is Hank Stauder. His stepfather changed his name after being fired for unauthorized human experimentation, founded Monstera, and hand-selected Emmett for the trial.
Resolved to expose Monstera, Emmett overdoses on 12 injector pens, dropping to 132 pounds. He posts an Instagram confession naming every victim, detailing the cover-ups, and revealing Hank's identity. At the Museum of Us, he photographs the Blount portrait, whose donor plaque credits Cecil H. Smith. His mother, Joanna, flies in from Las Vegas and waits outside with Lizette.
Police flood the museum. Emmett flees up California Tower as stress reactivates the Obexity in his bloodstream, ballooning his body grotesquely. On the viewing deck, Hank claims he created Obexity as redemption for people whom diet and exercise could never save. Emmett refuses to retract his post. Naked and enormous, estimated at 750 to 800 pounds, he shouts, "This is the true me!" and charges. Bautista shoots him three times. Emmett crashes through a broken railing and falls nearly 200 feet, pulling Hank with him. He dies on impact in the courtyard, before his mother and Lizette. Hank survives.
The novel's closing documents reveal that Emmett's warnings go unheeded. The investigative report concludes he was "inherently depraved," citing his childhood bite of Hank's hand as proof of preexisting violent tendencies, and absolves Monstera. A final letter reveals Smith's appointment as director of the FDA's Center for Drug Evaluation and Research (CDER). In this capacity, he overturns the previous denial and grants full approval for Obexity. His sign-off, "For the health and happiness of the country," echoes the corporate slogan, confirming that Emmett's abuser now controls both the drug that destroyed him and the institution meant to protect the public.