Kevin is a fourteen-year-old eighth grader who views lying as an essential tool to control social expectations. He considers himself highly intelligent and charismatic, often analyzing school dynamics with tactical precision. Armed with a large collection of military history books, he approaches his goals like a general planning a campaign. His overconfidence frequently blinds him to how his dishonest actions actually affect the people around him.

JonPaul is Kevin's best friend and a fellow eighth grader. He plays three team sports despite suffering from severe germophobia, hypochondria, and compulsive behaviors regarding his health. He relies on Kevin to help him research various medical conditions online, making him an easy target for Kevin's deceptive manipulations.

Katie is an ambitious and highly intelligent eighth grader with a strong work ethic. She approaches schoolwork seriously and is extremely trusting of others. Her sympathetic nature makes her quick to take on extra work when she believes a classmate is struggling with illness.

Daniel is Kevin's fifteen-year-old older brother. He shares ownership of a car with his siblings but lacks a driver's license, leading to frustration and arguments over how the vehicle is used. He is quick to feel slighted by his sister's control over the keys.

Sarah is Kevin's sixteen-year-old older sister and the only sibling with a driver's license. She leverages her legal ability to drive to maintain control over the car their aunt gifted them. Her strict rules about giving rides cause intense resentment among her younger brothers.

Auntie Buzz is Kevin's maternal aunt who lives in the apartment above the Spencer family's garage. She is an energetic, larger-than-life woman who has been married three and a half times. Though highly confident and charismatic, she struggles significantly with procrastination and managing her personal finances.

Markie is the Spencers' four-year-old neighbor. Though Kevin frequently describes him as exasperating and mischievous, Markie is deeply vulnerable due to his parents' ongoing marital issues. He desperately seeks honesty and clarity from the adults and older kids in his life.

Tina is an eighth-grade girl whom Kevin has known since preschool. She is civic-minded, heavily involved in student government, and generally well-liked. She serves as the primary motivation for many of Kevin's complex strategic maneuvers as he attempts to win her affection.

Connie is Tina Zabinski's best friend and a dedicated member of the student government. She is passionate about presenting ideas to the school board, making her an unwitting pawn in Kevin's plan to get closer to Tina.

Mom is Kevin's mother, who works long hours at a bookstore and provides her family with a constant supply of reading material. She is frustrated by her husband's constant absence and the growing emotional distance between her children. Her stress mounts as the week progresses, leading to significant household tension.

Dad is Kevin's father, whose demanding job keeps him away from home on business trips. His frequent absences leave him detached from the daily realities of his household, causing significant tension in his marriage. He is so out of the loop that he does not even realize his family owns a cat.

Mr. Crosby is Kevin's eighth-grade social studies teacher. He assigns a comprehensive research project on census data for underserved populations, unintentionally triggering Kevin's elaborate web of lies to avoid the work.

Señora Lucia is Kevin's Spanish teacher. She easily believes his fabricated story about becoming a student manager for the wrestling team, granting him permission to miss her class for several days.

Coach Gifford is the school gym teacher and wrestling coach. Kevin uses both the sports section of the newspaper and the wrestling team as cover stories to manipulate his class attendance.