Derek is a 12-year-old boy living in California who prefers reading *Calvin & Hobbes* comic books over chapter books. Labeled a reluctant reader by his teachers, he uses his passion for illustration to understand words visually rather than writing out definitions. He dreads the summer reading list assigned by his teacher, hoping instead for a season of relaxation, skateboarding, and investigating a mysterious old newspaper clipping he found in the attic.

A busy veterinarian, Derek's mother constantly balances demanding clinical work with her son's chaotic behavior. She strictly regulates Derek's summer, enrolling him in Learning Camp after discovering he dressed a clinic monkey in a cowboy outfit. Despite her frustration with his antics, she shows deep patience and harbors a heavy emotional burden regarding a decade-old drowning in Martha's Vineyard.

Working as a storyboard illustrator for movies, Derek's father sketches scenes for horror films. He is a primary source of inspiration for his son, who models his vocabulary drawings after his father's storyboards. He currently faces professional anxiety, feeling outpaced by younger artists using digital animation tools.

Matt is Derek's immature, highly agreeable best friend. The two boys spend their free time skateboarding, creating elaborate outdoor games, and actively avoiding summer homework. Matt leaves California for a family vacation on the East Coast, traveling to the exact location Derek wants to investigate.

Regarded as the smartest girl in Derek's class, Carly enthusiastically completes the summer reading list and volunteers to care for the class hedgehog, Ginger. Derek initially views her as an irritating overachiever, especially when they end up at the same summer Learning Camp, but he eventually discovers her hidden talent for building elaborate indoor obstacle courses.

Derek's English teacher presents an enthusiastic approach to learning that clashes with Derek's reluctance. Determined to help him succeed, she gives him an individually annotated novel filled with margin prompts to guide his reading. Outside the classroom, she surprises Derek by wearing casual clothes and playing softball at the local park.

A lively camp counselor at Learning Camp, Margot holds a strong distaste for traditional, forced reading lists. Recognizing Derek's visual learning style, she teaches him to picture paragraphs like scenes in a movie, a strategy that helps him engage with pictureless novels.

A teenager from Martha's Vineyard who drowned in a dangerous riptide ten years prior to the events of the novel. Her death becomes the central mystery of Derek's summer when he discovers her obituary hidden in his attic.

Derek's affectionate and slightly slobbery pet dog. Bodi accompanies Derek on neighborhood walks, provides emotional comfort during stressful moments, and even travels with the family on their East Coast vacation.

Derek's teenage babysitter who has grown out of wanting to actually play with him. She prefers watching television and chatting on her phone with friends, making her a frequent target for Derek's indoor bicycle stunts and general irritation.

A small capuchin monkey undergoing intense training to become an assistant for a teenager in a wheelchair. Derek temporarily steals Pedro from his mother's clinic, dressing him in a toy cowboy outfit and placing him on Bodi's back.

A 17-year-old boy living with cerebral palsy. He utilizes Pedro's trained skills to gain independence. Highly skilled with computers, Michael introduces Derek to animation software, transforming Derek's static vocabulary drawings into moving pictures.

Derek's grandmother resides in Boston and eagerly anticipates family visits. She pampers Derek extensively, offering to rub his feet and read his chapter books aloud, allowing him to enjoy feeling like a small child again.

Susan James's grieving mother, who meticulously maintains a memorial website dedicated to her daughter ten years after her death. Her living room features a massive collage of Susan's photos, showing she remains deeply anchored to the past.

A local artisan in Martha's Vineyard who was close friends with Susan James. She was present at South Beach on the day Susan drowned and carries vivid memories of the incident.

A physically large, intimidating classmate of Derek's known for having Cheeto-breath. He enjoys writing strange fantasy stories about chimpanzees with fruit allergies and occasionally threatens younger students with large rocks.

Matt's older brother, who manages a store at the mall. He indulges the younger boys' imaginations, allowing them to roll under the store's security gate pretending to be spies while his manager steps out.

The school classroom's pet hedgehog. Carly volunteers to take Ginger home over the break, tending to the small animal's daily needs.