Stanley is a fourteen-year-old boy from a low-income family who struggles with his weight and social isolation. He is wrongfully convicted of stealing a famous baseball player's sneakers. Given a choice by the judge, he serves his 18-month sentence at Camp Green Lake over a traditional jail. He blames his constant bad luck on a curse stemming from his great-great-grandfather.

Zero is the smallest and fastest hole-digger in Group D at Camp Green Lake. He rarely speaks and is constantly mocked by the counselors. Other campers treat him as though he lacks intelligence. Despite his tough exterior, he harbors a desire to learn.

The Warden is the fierce authority figure who runs Camp Green Lake. She forces the boys to dig large holes every day in the hot sun under the guise of building character. She closely monitors their progress for any interesting items they unearth and rules the camp through fear.

Katherine Barlow is a notorious 19th-century outlaw known for leaving a lipstick kiss on her victims. Family legends state she robbed Stanley's ancestor in the desert. Historical flashbacks reveal her actual past as a beloved schoolteacher in the flourishing town of Green Lake who made highly sought-after spiced peaches.

X-Ray is the unofficial leader of the Group D boys at Camp Green Lake. Though he is small and wears thick glasses, he commands respect from the other boys. He establishes the social hierarchy, dictating the order in which they get water and who takes credit for discoveries.

Sam is a kind Black man who sells onions from his donkey cart in historic Green Lake. He is knowledgeable about the healing properties of his crops. He frequently repairs the local schoolhouse to spend time with the local teacher.

Mr. Sir is a gruff leader at Camp Green Lake who constantly eats sunflower seeds after quitting smoking. He enforces the camp's strict rules. He shows little sympathy for the boys toiling in the heat and frequently reminds them they are not at a Girl Scout camp.

Mr. Pendanski is the counselor for Group D who initially appears more friendly than Mr. Sir, earning him the nickname "Mom" from the boys. His pleasant demeanor hides a cruel streak, particularly in his relentless mockery of Zero's intelligence.

Elya Yelnats is Stanley's great-great-grandfather, a young man who desperately wants to marry a beautiful local girl. He seeks magical assistance to secure a dowry. His failure to fulfill a subsequent promise results in a lasting family curse.

Madame Zeroni is an elderly woman with missing limbs who offers wise, practical advice. She provides Elya with a piglet to help him win a bride. She demands only that he carry her up a mountain to drink from a special stream in return.

Trout Walker is a wealthy, arrogant man in 19th-century Green Lake who smells strongly of fish due to a foot condition. He believes his money entitles him to whatever he wants. He grows vicious when rejected by the local schoolteacher.

Squid is a member of Group D at Camp Green Lake who follows X-Ray's lead. He acts tough during the day but struggles emotionally at night. He defensively denies his vulnerability when confronted.

Armpit is a physically imposing boy in Group D who is fiercely protective of his nickname. He enforces the group's social rules. He backs up X-Ray's authority when new campers arrive.

Zigzag is a tall boy in Group D with a volatile temper. He is fiercely territorial about his work. He is quick to turn on others when he feels slighted in the harsh camp environment.

Magnet is a camper in Group D who earned his nickname because of his tendency to steal things. He claims his fingers act like magnets. His opportunistic theft gets others into trouble.

Clyde Livingston is a famous, highly successful baseball player known as "Sweet Feet." His donated sneakers are stolen from a homeless shelter auction. This theft leads to Stanley's wrongful conviction.

Stanley's Father is an intelligent but historically unlucky inventor trying to create a way to recycle used sneakers. He maintains a positive attitude despite his lack of success. He firmly believes that not everyone in his family is doomed by the ancient curse.

Stanley's Mother is a supportive parent who tries to stay optimistic about her son's situation. She writes him letters pretending he is at a normal summer camp. She frequently worries about their impending eviction due to her husband's smelly shoe experiments.

Mary Lou is a loyal donkey belonging to the onion seller in 19th-century Green Lake. She pulls the cart full of onions. She is deeply loved by her owner, who feeds her a special diet.

Myra Menke is a beautiful but empty-headed young woman in Elya Yelnats's village. She struggles to make simple decisions. Her inability to choose a suitor heavily frustrates Elya.

Derrick Dunne is a bully at Stanley's middle school who relentlessly torments him. Despite being smaller than Stanley, he frequently harasses him, including throwing his notebook in the toilet on the day of Stanley's arrest.