Set during the COVID-19 pandemic, this middle-grade horror novel follows twelve-year-old Casey Wilson, a lonely sixth grader whose life is upended when a strange clay figure arrives at his home and begins slowly replacing him.
Casey lives with his parents while his older sister, Ally, is away at college. The family owns an antique rotary phone kept for emergencies because it works without electricity or cell service. One Wednesday during April vacation, the phone rings despite its ringer being turned off. Mom answers and arranges for someone's son to visit, though she cannot recall the caller's name. Casey has no idea who would come: His friends abandoned him after what Dad calls "the Zoom Incident." Earlier that year, a classmate recorded Casey's involuntary facial tics during a virtual class, set the video to music, and posted it online. The video went viral, and Casey's friends stopped contacting him.
That afternoon, a short man in a flat cap arrives with a dusty burlap sack. He blows gray dust into the parents' faces, causing momentary confusion when they turn to Casey, as if they do not recognize him. A boy-shaped figure emerges from the sack: a living mannequin with pinkish-gray, clay-like skin and only ridges where facial features should be. The man introduces him as Morel, calls him Casey's "new friend," says Morel requires "no food" and "no bed," and leaves. The parents accept everything without protest.
Casey feels danger but is also thrilled by the strangeness. The two bond over drawing, Casey's greatest talent. Casey sketches Morel as a mountain lion and an owl. When Casey tries to photograph him, Morel smacks the phone away. Casey apologizes, recognizing how violating it is to have one's image taken without consent. At dinner, the parents fawn over Morel. That night, Casey hears Morel rise from the beanbag chair in the dark. Paralyzed, he feels a stinging itch on the back of his head before Morel settles again.
Over the following days, Morel transforms. His face gains the ability to move on its own. He asks Casey to draw an anatomical heart and a small image representing speech, then places both inside his clay body. Soon Morel speaks for the first time, his voice identical to Casey's. Meanwhile, Casey deteriorates: puffy eyes, grayish lips, swollen fingers. His parents grow cold, with Dad yelling at him during baseball practice and neither parent acknowledging him at home. Casey shows Morel a schematic from a neuropsych evaluation, a diagram of overlapping shapes that Casey copied imperfectly, revealing executive functioning difficulties. He later catches Morel eating the schematic page. Morel claims he was removing a "bad reminder."
Ally, viewing a photo Casey sent, calls Morel Casey's "doppelgänger," or look-alike. She texts that when Casey draws, he looks like "the FULL you." One night, Casey wakes covered in hyphae, tube-like fungal structures stretching from Morel across the room, glowing in the dark. He feels himself dissolving and thrashes until the hyphae detach. Morel, now dripping with writhing hyphae, rolls Casey to face the wall and insists he merely had a nightmare.
Casey researches online and learns that morels are a species of fungus and that parasitic fungi grow hyphae networks to drain nutrients from hosts. He draws a humanoid figure made of twisted hyphae, and the act of drawing unlocks his suppressed memories of the attack. He confronts Morel, who insists, "I'm not a monster." Casey sleeps in Ally's locked room but wakes cocooned in hyphae, the door forced open, a shadow-eyed figure crawling toward him. He loses consciousness.
Casey wakes with almost no memory. Morel now looks nearly identical to him, with uncannily smooth skin. Dad addresses Morel as "Casey" and takes him to the baseball game in Casey's uniform. When Casey protests, Mom dismisses it. Alone, Casey discovers his own skin indents like clay when pressed. Ally, viewing a selfie, says he looks like a mannequin. Dad returns crying while cheerfully recounting Morel's performance. At dinner, no plate is set for Casey, and Dad announces a new rule from Morel's father: "No drawing."
That night, Morel tells Casey his origin story. He woke in an underground cavern with walls of glowing hyphae, his own body made of clay. The man emerged from the tunnel wall itself, told Morel everything about Casey, and said it was okay for Morel to "borrow" from him. Casey summons one word from deep inside, "No," spoken in his own true voice. He imagines this piece of himself as a small fire he must protect.
The next morning, Casey's body has fully transformed to clay, his mouth sealed shut. Mom calls him "Morel." But when she hands him a pen, the feel of it triggers something. Casey begins sketching, and memories flood back. He remembers Ally's words about looking like his full self when he draws. Drawing is bringing Casey back. He recalls the spores, the hyphae attacks, his fungal research. He puts on a medical mask, opens windows, and prepares two drawings: a deliberately wobbly re-creation of the schematic and a family portrait showing Ally's new snake tattoo.
When Dad, Morel, and the man arrive, Casey holds up a written message: "I am Casey and I can prove it." He displays his drawings, then hands Morel the pencil. Morel produces only a crude stick figure, proving he cannot draw. The parents stagger toward Casey, beginning to recognize him. The man shoots a strand of hypha to yank the phone off the hook, flooding the room with spores. The parents collapse. The man wraps Morel in hyphae and urges Casey to come willingly, promising Morel will be "the perfect version" of Casey while Casey joins the fungal network.
Casey holds up a note to Morel referencing a
Legend of Zelda move he once taught him. Morel leaps at the man's legs and knocks him down. Casey grabs the phone, runs outside, and smashes it with a rock. Beneath the crushed device lies the deflated flesh of a large mushroom. Inside, the man screams in agony and flees.
Morel tells Casey the real him is still underneath the clay. Casey peels back the fungal layer on his forearm and finds his own skin beneath. He frees his hands, then his face, laughing at his own voice. Morel returns the schematic he ate, having dug it from his own body. Morel, already reverting toward his unfinished appearance, asks to keep Casey's drawings. He must find the man and discover who he was before waking in the cavern. He calls it "a real-life Zelda quest" and disappears.
The parents stir awake, sneezing as the spores clear. Casey showers and cleans the house. Dad hugs him and says, "I love you, buddy." Casey never blames his parents but understands they cannot always protect him. A month later, his facial tics have faded. He has joined the school art club and eats lunch with new friends. When Ally returns for summer, she reveals a second tattoo: Casey's heart drawing. In a final scene, a boy in a green baseball hat steals a bizarre white rotary phone from an antiques store, a phone recently donated by a man in a flat cap, suggesting Morel's quest to stop the man continues.