Thirteen-year-old Kate Tyler lives on a chicken farm on the Eastern Shore of Maryland, where her family raises tens of thousands of broiler chickens under contract for Valley Shore Chicken Farms. The novel opens at Arlington National Cemetery on a warm October day, as Kate, her five-year-old sister Kerry, their mother Angela, and their grandmother Sarah Gunter attend the military funeral of Kate's father, Jacob Tyler. Kate's older brother, J.T., is absent: Their mother has forbidden him from attending because he is serving time at a juvenile detention center called Cliffside for his role in a prank that caused the death of a young boy named Benjamin DiAngelo. Yet during taps, Kate glimpses J.T. on a distant hill, trumpet in hand. She has secretly arranged his presence by lying to his counselor, retrieving the trumpet from J.T.'s sealed bedroom, and mailing it to the detention center to fulfill her father's dying wish. After the ceremony, Angela collapses from a panic attack, and Kate reflects that this first deception may have been where her "own downfall began."
Over the nine months of J.T.'s detention, Kate writes him 28 letters without receiving a response. She takes on responsibilities far beyond her age: grocery shopping with the help of her best friend Jess Jones's mother because Angela has developed agoraphobia, a condition that prevents her from leaving the house; cooking meals from index cards she and her grandmother created; and caring for Kerry. When J.T. is finally released in late May, the reunion is strained. Angela stands with brownies but cannot say welcome. Kerry, now six, breaks the silence by asking why their mother will not talk to J.T. Angela admits she is trying to forgive him, but the wound remains open.
Summer brings gradual healing. J.T. takes over all farm chores from Uncle Ray, Kate's uncle, and his electronic ankle bracelet comes off in August. Kate rescues a three-legged baby rabbit she names Hoppy. She and J.T. reconnect, though he refuses to discuss his former best friend Brady Parks or to touch his trumpet again. Kate hopes high school will be a fresh start.
That hope shatters immediately. Kate, a year younger than her classmates because she skipped a grade, feels out of place. In the cafeteria, someone throws a milk carton at J.T. as he sits alone. Kate and Jess identify Curtis Jenkins, who bullied J.T. in middle school by calling him "Chicken Man," and his sidekick Hooper Delaney. The next morning, a banner reading "THE CHICKEN MAN RETURNS" hangs near J.T.'s locker. Kate tears it down and files a bullying report, but J.T. denies everything when called to guidance, fearing the attention will worsen matters.
The bullying escalates. Kids steal chairs so no one sits with J.T. at lunch, cluck at him in study hall, and stuff him into a gym locker. A Facebook page appears with his face pasted on a chicken's body. J.T. stays home on multiple days and confides to Kate that he sometimes wishes he were not alive. Then Curtis offers a deal: If Kate writes his Creative Writing assignment, he will leave J.T. alone. Kate initially refuses but, seeing J.T.'s despair, rationalizes that cheating for a good reason is justified. She writes a 250-word author bio about fishing on Curtis's behalf, and the bullying stops.
For weeks the arrangement works and J.T. seems happier. But Curtis demands more: a paper on the Nile River, then an essay on
Animal Farm. Each assignment forces Kate to neglect her own work. She fails a geometry quiz, is cut from the field hockey team, and stops attending newspaper meetings. Her friendship with Jess suffers because Kate cannot explain what consumes her time. Jess reveals that Curtis's older brother Justin was a soldier who visited their fifth-grade class and later died, suggesting Curtis's anger may stem from grief.
Angela, despite her agoraphobia, takes a taxi to the school to report vandalism of the family mailbox, which has been smashed and stuffed with chicken manure and a note calling J.T. "the Baby Killer." The assistant principal says the school cannot act on off-campus incidents, but the visit marks a step in Angela's recovery.
The cheating scheme recedes when J.T. suffers a severe tractor accident. While mowing with a Bush Hog, a powerful rotary mower, he hits a drainage ditch and falls off. The blades tear into his leg. Kate, nearby at the abandoned Beck farm where she has been secretly feeding chickens she has hidden there, spots the driverless tractor and races to help. She fashions a tourniquet from J.T.'s belt to slow the bleeding. Brady Parks, J.T.'s former best friend and next-door neighbor, arrives with his paramedic cousin. J.T. survives and keeps his leg, partly because Kate's imperfect tourniquet does not fully cut off blood flow.
While J.T. recovers, Kate must perform the culling alone, selecting and killing unfit chicks by breaking their necks. Unable to do it, she carries about 30 chicks to the Beck farm, adding them to the flock she has been hiding, and records everything in her journal. Angela later discovers the hidden chickens but reacts with empathy, revealing that she once tried to open the chicken house windows and Kate's father forbade her from going near the birds again. Mother and daughter share a moment of understanding about the moral conflicts of factory farming.
Curtis then reveals that the ongoing demands were never for him. Hooper needed the papers and had been blackmailing Curtis by threatening to expose that Justin had died by suicide rather than as the war hero their community believed. Hooper steals Kate's journal, which documents the hidden chickens and J.T.'s science project testing chicken manure for arsenic, and calls Valley Shore to report both. Company men arrive to inspect the property, but the coop is empty: Curtis has moved the chickens to his own home. Angela stands up to the inspectors, asking what they have to fear if they comply with the law.
In a family meeting, J.T. reveals he has shifted his research to antibiotics in chicken feed. Angela stuns everyone by proposing they use Jacob's life insurance to pay off the mortgage, end the Valley Shore contract, and start a cage-free, free-range egg business. The family agrees.
J.T. returns to school on crutches, with Brady organizing help in the hallways. Curtis visits the farm, and J.T. later tells Kate the conversation was "all ancient history." Hooper moves away to live with his mother. Curtis returns Kate's stolen journal. In spring, 500 Rhode Island Red chicks arrive, and the Tylers launch their new operation with open windows and outdoor yards. Angela drives to the post office to pick up the chicks, marking her continued recovery from agoraphobia.
In the final chapter, Kate considers confessing the cheating to the school principal. She approaches the open office door, recalling her father's advice that many things in life are not black and white but gray, and that you do the best you can for your family. When J.T. calls for help carrying a box, Kate turns away. The novel ends with Kate running to her brother, unrepentant but still conflicted, certain she loves her family and would cheat again if she had to.