The Tao Jones is a 17-year-old multiracial high school senior living in Cutter, Washington. Adopted by white parents as a toddler, he is a highly skilled athlete who refuses to participate in organized sports to protest the favored treatment of the school's athletes. He possesses a strong sense of justice and forms an unconventional swim team to challenge the social hierarchy of his high school.

John Paul is a physically imposing man who works on Harley motorcycles and serves as T.J.'s adoptive father. He possesses a deeply gentle nature and regularly volunteers his time to act as a supportive figure for abused children. He spends his life attempting to atone for a fatal accident from his past, relying on empathy to understand the most volatile people in his community.

Abby is T.J.'s adoptive mother and a dedicated juvenile court attorney. Her daily contact with abused children and their families informs her realistic, grounded perspective on human cruelty. She advocates fiercely for her son while teaching him to recognize the limits of intervening in dangerous situations.

Rich is a former athlete who runs his family's logging company. He functions as a dangerous presence in Cutter, harboring deep-seated racist views and frequently exhibiting abusive behavior toward his family. He holds a bitter grudge against T.J. stemming from an incident involving a baby deer years earlier.

Mike is a star football player at Cutter High and a quintessential bully. He embodies the toxic entitlement of the school's athletic programs, frequently using his physical size and social standing to intimidate vulnerable students. He aggressively polices who is allowed to wear athletic letter jackets.

Chris is a developmentally challenged student who suffers from the lingering effects of childhood abuse. He honors his deceased older brother by wearing his varsity letter jacket, which makes him a frequent target for school bullies. He becomes one of the earliest recruits for the Mermen swim team.

John is T.J.'s English teacher and a former competitive swimmer. When tasked with launching a new athletic program, he recruits T.J. to build a swim team from scratch. He advocates for his unconventional athletes against the school's entrenched sports establishment.

Coach Benson is the head football coach and a leader of the Athletic Council at Cutter High. He is a staunch defender of athletic privilege and the school's traditional hierarchy. His commitment to protecting his star players frequently blinds him to their abusive behavior.

Georgia is a play therapist and one of the few people of color living in the racially homogeneous town of Cutter. She helped T.J. manage his anger issues when he was younger and continues to offer him practical advice regarding his relationships and local conflicts.

Heidi is the biracial daughter of Alicia Marshall. Living with an abusive stepfather, she internalizes negative beliefs about her own skin color, leading to deep psychological trauma. She occasionally stays with the Jones family to escape the volatile environment of her home.

Alicia is the working-class wife of Rich Marshall. Struggling with low self-esteem and a lack of resources, she finds herself trapped in a cycle of domestic abuse. She frequently relies on social services and the Jones family to ensure the safety of her children.

Oliver, nicknamed "Icko," is an unhoused man who sleeps secretly in the local gym to save money for his son's college tuition. He steps in as the unofficial coach and bus driver for the Mermen. He provides the isolated boys with an unexpected source of adult support.

Carly is an athletic student who dates T.J. Having grown up in an affluent but physically abusive household, she establishes strict boundaries and refuses to tolerate controlling behavior. She provides T.J. with emotional stability and straightforward honesty.

Andy is an intimidating, surly student who lost part of his leg to gangrene following severe childhood abuse. He relies on a prosthetic leg and a caustic sense of humor to keep others at a distance before joining the swim team.

Jackie is the quietest member of the Mermen. Cut from the junior varsity football team, he rarely speaks out of fear that drawing attention to himself will cost him his newfound sense of belonging.

Simon is a dedicated but overweight student who joins the swim team. He struggles with body image issues but finds acceptance and camaraderie among his fellow misfit athletes.

Tay-Roy is a muscular, steroid-free bodybuilder and talented musician. Exhausted by the expenses and demands of bodybuilding, he joins the Mermen to stay active in a more supportive setting.

Dan is a highly intelligent student known for his expansive vocabulary and long-winded explanations. He brings a unique intellectual energy to the swim team.

Stacy is a widow from New Meadows, Idaho. Thirty years before the main events of the story, her life briefly intersected with John Paul's, leading to a profound tragedy that forever altered his worldview.

Tyler is the eighteen-month-old toddler whose accidental death decades ago serves as the foundational trauma of John Paul's adult life.

Kyle is a young man living in New Meadows, Idaho, who runs a whitewater rafting company. He crosses paths with T.J. during the summer following graduation and offers him summer employment.

Kristen is a high school student who dates Mike Barbour. She frequently experiences his violent temper firsthand, demonstrating the broader cycle of abuse present in the community.