Emily is a twelve-year-old girl whose parents move the family to a new state every year. She craves stability and dreads the constant disruption of her social life. To cope, she participates passionately in an online game called Book Scavenger, where players hide and locate books based on clues. Her virtual gaming community provides her with her only reliable sense of continuity.

James is an eccentric twelve-year-old boy living in San Francisco in a building his family has owned for generations. He enjoys puzzles and ciphers, communicating with Emily through an old bucket-and-pulley system suspended between their windows. He values his stable home life and offers Emily her first chance at a grounded, in-person friendship.

Matthew is Emily's teenage brother. He sports an asymmetrical Mohawk and obsesses over his favorite punk rock band, Flush. Unlike Emily, he adapts easily to their parents' nomadic lifestyle by maintaining long-distance friendships online. He is a former Book Scavenger player who has since outgrown the game.

Garrison Griswold is an elderly publisher and the creator of the Book Scavenger website. He believes in spreading enthusiasm for literature to as many people as possible. Early in the story, he suffers an attack in a transit station while carrying a special edition of an Edgar Allan Poe story, leaving his newest puzzle unsolved.

Leon Remora is a rare book collector with a rumpled appearance and thinning hair. He manages a private collection and values books purely as physical objects of prestige rather than as stories to be read. He intensely desires to possess Griswold's special edition book and hires men to track it down.

Hollister is an older Black man who wears his hair in dreadlocks. He owns and operates a small independent bookstore in San Francisco. He and Griswold were once business partners but parted ways over disagreements about expanding the store. He quietly watches out for the local children who visit his shop.

Barry is a hired thug working alongside his partner Clyde to retrieve a missing book. He is Leon Remora's nephew and takes orders from his uncle. While he actively pursues the target, he exhibits unease when his partner and uncle resort to extreme coldness or violence.

Clyde is a hired thug working with Barry to track down Griswold's missing book. He exhibits a cold and threatening demeanor during the pursuit. He carries a weapon and shows no hesitation about using intimidation to accomplish his goals.

Mr. Quisling is the social studies teacher at Booker Middle School. He maintains an intimidating presence in the classroom but possesses a genuine passion for historical ciphers and codes. He encourages his students to create their own puzzles for a class challenge.

Maddie is a middle school student in Mr. Quisling's social studies class. She acts harshly toward Emily and focuses heavily on beating James in a classroom cipher challenge. She cares more about seeing James lose than actually winning the contest herself.

Jack Kerouac is Garrison Griswold's personal assistant at Bayside Press. Despite his famous name, he has no relation to the well-known author. He manages Griswold's office and interacts with fans who arrive claiming to have solved the latest puzzles.

Ms. Lee is the landlady of the apartment building where the Crane family rents a unit. She belongs to the Asian American family that has held the property for generations. She interacts briefly with the new tenants to enforce building rules.

Emily and Matthew's parents are adventurous writers who uproot their family every year. They are writing a blog and book about living in all fifty states. They enjoy the excitement of constant travel but fail to recognize the emotional strain this lifestyle places on their daughter.

Raven is a mysterious figure on the Book Scavenger online forums. Emily reaches out to this user for help decoding clues related to Edgar Allan Poe's writings. Raven responds with cryptic hints that push Emily to look deeper into the puzzle.