Flora is a 10-year-old self-proclaimed cynic who relies on comic books to cope with her life following her parents' divorce. She possesses a vivid imagination and a resourceful nature, often visualizing conversations as comic book speech bubbles. Her practical exterior masks a deep loneliness, which begins to dissipate when she rescues an unusual squirrel with extraordinary abilities.

Ulysses is an ordinary squirrel who gains human-like understanding and extraordinary physical abilities after a bizarre accident with a Ulysses 2000X vacuum. Though he retains typical squirrel instincts, such as a deep preoccupation with food, he quickly develops an appreciation for poetry and a strong affection for his rescuer. He views his newfound awareness as an illumination, finding sudden beauty in everyday objects.

Phyllis is Flora's mother, a romance novelist who struggles to connect with her pragmatic daughter. Highly focused on her writing and maintaining a sense of normalcy, she views Flora's comic book obsession as a distraction from proper literature. Her controlling tendencies and immediate distrust of the super-powered squirrel place her in direct opposition to Flora.

William is an 11-year-old boy spending the summer with his great-aunt after his mother sent him away from home. He presents himself as temporarily blind, constantly wearing dark glasses and speaking in highly formal sentences. He approaches life with skepticism and scientific logic, serving as an intellectual foil to Flora's comic-book worldview.

George is Flora's father, an accountant who has grown quiet and melancholic since his divorce. He previously shared a strong bond with his daughter through their mutual love of superhero stories, a connection that has frayed as he retreated into sadness. Witnessing a flying squirrel begins to reawaken his buried sense of joy and laughter.

Dr. Meescham is a Doctor of Philosophy who resides in George Buckman's apartment complex. She maintains a deeply optimistic and open-minded view of the world, keeping her window open to invite unexpected miracles. She acts as a wise, comforting presence who encourages others to embrace the beauty of the impossible.

Tootie is a neighbor of the Buckman family who accidentally sets the story in motion through a yard work mishap. She is an adventurous, dramatic woman who quickly embraces the strange events happening around her. She provides shelter and support for her great-nephew during his summer stay.

Donald is Tootie's husband, a practical man who inadvertently causes chaos by purchasing a Ulysses 2000X vacuum cleaner. He encourages his wife to test the industrial-strength machine outside, leading directly to the incident that grants the squirrel his powers.

Rita is a waitress at a local diner who Flora thinks resembles Marie Antoinette. She serves Flora and George during their lunch outing and becomes entangled in the chaotic public revelation of a squirrel's unusual abilities.

Mr. Klaus is the aggressively territorial cat belonging to the apartment landlord. He actively terrorizes the tenants, frequently ambushing people in the hallways and targeting their ankles.