Emily’s best friend, James is a cheerful and intelligent classmate who shares her enthusiasm for books and puzzles, and participates in their collaborative investigations.

Emily’s social studies teacher, he is a complex character with a personal connection to the Book Scavenger game, initially giving an impression of secrecy and mystery.

The novel’s antagonist, Mr. Sloan is a former teacher who uses the persona of "The Phoenix" to execute a plan of revenge involving a series of arson attacks.

Emily’s charismatic older brother, Matthew provides support and contrasting confidence to Emily, joining her and James on significant adventures.

The owner of a bookstore, Hollister is a mentor figure to Emily, who provides her with a welcoming environment to explore her passion for books.

The founder of Book Scavenger, Mr. Griswold is a once-flamboyant character who becomes more reclusive after an attack but is encouraged by Emily to rejoin the community.

A college student working on Hollister’s website, Charlie is a red herring in the mystery who faces repercussions for his dishonesty and irresponsibility.

Adventurous freelancers who frequently move the family, creating tension with Emily’s desire for stability, but remain supportive and considerate of her wishes.

An unconventional green-haired librarian at the History Center, Ms. Linden aids Emily with her knowledge of local history and represents a free-spirited adult mentor.