Arthur is a highly intelligent former academic who has confined himself to the ground floor of his Brooklyn brownstone for a decade. Weighing over 500 pounds, he relies entirely on online deliveries and maintains a rigid routine to avoid the outside world. He protects himself from further emotional pain by refusing visitors and creating elaborate fictions about his daily life to hide his isolation.

Kel is a 17-year-old high school senior and star baseball player moving between two vastly different social circles. He lives in working-class Yonkers, where he acts as the primary caregiver for his chronically ill mother. At the same time, he attends school in the affluent suburb of Pells Landing, adopting the clothing and mannerisms of his wealthy peers to conceal his difficult home life. He relies on his athletic talent as his primary hope for achieving financial stability.

Charlene is Kel's mother and Arthur's former student, currently living in Yonkers. She suffers from lupus and relies heavily on alcohol to cope with her physical and emotional pain. Her deteriorating health forces her son to take on significant caretaking responsibilities. She attempts to secure a better future for him by enrolling him in a prestigious high school outside their neighborhood.

Yolanda is a 19-year-old woman working for a cleaning agency who is assigned to Arthur's house. She arrives wearing an ill-fitting uniform and brings a pragmatic, nonjudgmental attitude to the massive task of cleaning the neglected brownstone. Her presence forces Arthur to confront his living situation and consider letting someone into his private space.

Lindsay is a popular field hockey player in Kel's class at Pells Landing High School. She comes from an affluent, stable family, with a father who serves as the school superintendent and a mother who works as a lawyer. She shows genuine interest in Kel, providing him a glimpse of a comfortable life outside of Yonkers.

Francis is the man Kel knows as his father, who left the family when Kel was four years old. Kel holds onto his old high school sports trophies and Mets memorabilia, building an idealized image of him to cope with his long absence.

Trevor is Kel's wealthy best friend at Pells Landing High School. He comes from a privileged background and represents the comfortable suburban life that Kel tries to assimilate into during school hours. He provides Kel with a social anchor at the new school.

Dee is a skilled quarterback for Yonkers High School and Kel's childhood friend. Their relationship became strained after Kel transferred to Pells Landing, but they maintain a complex bond rooted in their shared neighborhood and history.

Junior is Yolanda's boyfriend, described as a muscular young man with tattoos and a bandanna. He lacks steady employment and has a volatile relationship with Yolanda that frequently causes her emotional distress.

Marty is Arthur's former best friend and neighbor who previously helped Arthur secure his academic job. He represents the lively, socially engaged past that Arthur left behind following his professional scandal.

Matt is a student at Pells Landing High School and Lindsay's ex-boyfriend. He views Kel with suspicion and operates within the affluent social circles of the school, creating tension when Kel begins spending time with Lindsay.

Kurt is one of Kel's affluent classmates at Pells Landing High School. He runs in the same privileged circles as Trevor Cohen and views Kel's Yonkers background with a mix of curiosity and distance.

Jeanie is Lindsay's mother and a successful lawyer in Pells Landing. Her warm, stable home environment provides a sharp contrast to the chaotic reality Kel experiences in Yonkers.

Gerard is a talent scout for the New York Mets who holds significant influence over Kel's future. He schedules a private evaluation to test Kel's potential for professional sports, representing Kel's primary hope for financial security.