Daniel "Skippy" Juster is a 14-year-old, second-year boarding student at Seabrook College. He struggles under the weight of his mother's undisclosed illness and the mounting pressure from his competitive swim team, relying heavily on painkillers to get through his daily routine. Despite his growing isolation and anxiety, he finds a spark of hope when he develops a crush on Lorelei "Lori" Wakeham, a girl from a neighboring school.

Howard is a history teacher at his alma mater, Seabrook College, having left a lucrative but exhausting career in finance. He fears settling into a monotonous life, leading to increasing tension with his long-term girlfriend, Halley. His desire for excitement and change manifests as a growing infatuation with the school's new substitute geography teacher, Aurelie McIntyre.

Ruprecht is an eccentric, highly intelligent student at Seabrook College who shares a room with Skippy. Obsessed with M-theory and the origins of the universe, he spends his time designing complex scientific experiments to contact alien civilizations and open portals to parallel dimensions. He maintains a fabricated backstory, telling his peers that his aristocratic parents were lost during an expedition in the Amazon.

Lori is a student at St. Brigid's, the neighboring girls' school. Despite her outward popularity and attractive appearance, she struggles with low self-esteem and harbors frustrations with her family's materialism. She becomes entangled with Carl Cullen to obtain what she believes are diet pills, though she soon captures Skippy's genuine affection.

Carl is a ruthless bully and aspiring drug dealer at Seabrook College. He uses stolen prescription medication to build a small dealing operation targeting the girls at St. Brigid's. His business ambitions are heavily motivated by his aggressive desire to initiate a physical relationship with Lori, bringing him into direct conflict with Skippy.

Known as "the Automator," Greg is the acting principal of Seabrook College. He represents the school's transition from clerical to lay leadership. He is highly focused on managing the institution's public image, courting corporate donors, and maintaining strict control over his teaching staff.

Father Green is a strict, old-fashioned priest and French teacher at Seabrook College. A former missionary in Africa, he views the modern world with intense disdain and harbors deeply conflicted, inappropriate feelings about desire and salvation, which he projects onto vulnerable students.

Aurelie is a glamorous substitute geography teacher at Seabrook College who previously worked as an investment banker. She takes a pragmatic, straightforward approach to her interactions with her colleagues, directly informing an infatuated Howard that she has no intention of sleeping with him upon their first meaningful conversation.

Halley is Howard's American girlfriend who works writing office hardware reviews. She is eager to settle down, get married, and secure her life and visa in Dublin. This desire for stability puts her at odds with Howard's growing fear of commitment and domestic routine.

Tom is the somber swim team coach at Seabrook College. A former star athlete whose promising career was derailed by a bungee-jumping accident in his youth, he now pushes his swimmers relentlessly. He maintains an intense focus on Skippy's performance and privately supplies the boy with painkillers.

Barry is Carl's best friend and loyal sidekick. He lacks Carl's aggressive edge but eagerly participates in their scheme to sell stolen prescription pills to the girls at St. Brigid's, viewing it as an easy business opportunity to acquire branded goods.

Dennis is a deeply cynical student at Seabrook College who frequently clashes with Ruprecht. He serves as the primary skeptic in their friend group, constantly mocking Ruprecht's scientific theories and attempting to puncture his romantic worldview.

Geoff is one of Skippy and Ruprecht's loyal friends. He enthusiastically supports his friends' endeavors, whether he is helping Skippy compose a haiku to impress Lori or participating in Ruprecht's eccentric musical and scientific projects.

Mario is a core member of Skippy's close-knit social circle at Seabrook College. Resourceful and occasionally mischievous, he is the one who successfully manages to acquire Lori's phone number so Skippy can contact her.

Farley is a biology teacher at Seabrook College and one of Howard's closest friends on the staff. He serves as a voice of reason, repeatedly warning Howard against jeopardizing his stable relationship with Halley for a fleeting workplace crush.

Jim is an older teacher at Seabrook College who once taught Howard when Howard was a student. His past humiliation following a difficult divorce serves as a living cautionary tale for Howard about the dangers of domestic failure.

Janine is a student at St. Brigid's and Lori's close friend. She acts as an intermediary, carrying messages and coordinating interactions between Lori and the boys from Seabrook, often facilitating Carl's access to Lori.

Gavin is Lori's highly protective and materialistic father. He sets strict rules for his daughter and frequently clashes with her over her social life, attempting to maintain absolute control over her choices and behavior.

Skippy's father struggles to maintain a sense of normalcy at home while concealing his wife's cancer diagnosis. He dismisses Skippy's requests to come home early from school and encourages his son to push through his difficulties, prioritizing routine over emotional honesty.

Skippy's mother is suffering from cancer, a fact that her husband insists on keeping hidden from the school community. Her illness places an enormous silent burden on Skippy, who feels unable to share his grief with anyone at Seabrook.