Milo is a clumsy preadolescent boy who struggles with low self-esteem and considers himself a total klutz. Living with his parents and older sister, he frequently faces teasing and scolding for minor accidents like sitting on records or dropping groceries. Eager to escape his daily embarrassments, he commits to following a bizarre three-day program to achieve absolute perfection.

Dr. Silverfish is the sarcastic author of the guidebook Milo discovers. Claiming to be an expert on perfection, he presents an absurd public image, wearing a clown nose, half a bow tie, one mitten, and baggy pants. He communicates with his readers through an unconventional, mind-reading instructional style that challenges their assumptions.

Elissa is Milo's older sister. She engages in constant sibling rivalry, frequently calling Milo a pest or stupid for his clumsy mistakes. Her sharp comments feed directly into Milo's insecurities and drive his desire to become completely flawless.

Mr. Crinkley is Milo's father. While he participates in correcting Milo's daily behavior, he also holds realistic expectations about human flaws, noting that nobody is perfect. He pays close attention to his son's unusual new habits at home.

Mrs. Crinkley is Milo's mother. She manages a household frequently disrupted by Milo's accidents, such as breaking her expensive vase or dropping full grocery bags. She regularly corrects his behavior, which makes him feel inadequate.

George is the class bully at Milo's middle school. He relies on intimidation and mockery to exert power over his classmates. He specifically targets Milo when Milo arrives at school acting strangely to complete his first perfection task.

Janet is a classmate of Milo. She is quick to judge others and verbally expresses her disapproval when Milo breaks social norms at school by wearing a stalk of broccoli.