Violet Bookman. Fearless, inquisitive, though often lacking in confidence, seventeen-year-old high-schooler Violet wants to discover the truth of the town's recent disappearances. When her best friend's cat goes missing, Violet embarks on a journey that leads her deeper into the secrets of the town while also bringing her closer and closer to danger.
Nanako Yakamoto. A twelve-year-old cello prodigy and Violet's best friend, Nanako loves creating her own board games and accompanying Violet on her investigations throughout town. When her beloved cat, Mr. Business, goes missing Violet and Nanako begin a search through town to find the answer to all of the recent disappearances.
Iris Englebrecht. Eighteen-year-old high school senior Iris is fascinated by ghosts, the occult, and unsolvable mysteries while keeping her own secrets about her past in the nearby town of Marietta, Ohio. A close friend and ally of Violet, the two unravel the historical mysteries surrounding The Void, nearly win a car contest, and become momentary owners of the Upside-Down House. At the same time, Iris refers to getting revenge on an unknown person or persons in town.
Bruno Ellis. The silent, enormous Department of Streets and Sanitation worker is one of Violet’s closest allies. A former amateur wrestler, Bruno served time in the 1980s for accidentally killing an opponent in the ring. He communicates exclusively through hand-written notes.
Ron Dublowski. A forty-nine-year-old Question Mark police officer who, too late, may have realized he would rather be a record producer, Ron often feels overwhelmed when facing the accumulating mysteries and disappearances the town must face. A devoted husband and father and member of the KISS Army, Ron soon comes to understand his purpose, with Violet’s help, as larger and larger challenges overtake the town.
Holly Peterson. Quiet, poetic, and brave, third-grade teacher at Question Mark Elementary Holly often wanders the town alone at night in search of the ghost of her younger brother. Holly offers Violet guidance, reveals important clues, and gives critical advice about living with loss.
Greta Twombley. Resolute and kindly, Ms. Twombley is Question Mark Public Library’s head librarian and is committed to helping Violet ask tough questions about the town. Facing the recent death of her husband, Bill, and navigating a difficult pregnancy, Greta challenges Violet to continue her search for answers.
Mayor Elizabeth Zisk. Complicated, cunning, and uncompromising, Elizabeth Zisk is Question Mark’s longest-serving mayor. After the tragic death of her husband, Thompson Zisk, Mayor Zisk has led the town through a series of crises, from large to small, all while managing to reveal very little about her private life or past. As catastrophes begin to build, Mayor Zisk is forced to decide between her own ambitions and the survival of the town.
The Purple Light. Whether a ghost, an escaped specimen from the Experimental Crop Station, or some other unknown entity, Violet first encounters the purple light in the woods after it is attracted to the sound of the music she is playing. Armed with invisible tentacles, this odd creature feeds on light, responds to the nickname Q-eey, and may hold the secret to the town's disappearances.
FBI Agent Adam Oberman. After six-year-old Quentin Quinn goes missing, Agent Oberman arrives in town from Columbus to participate in the investigation. He quickly admits his doubts about being an FBI agent, suggesting he would have preferred a life in musical theatre. Thoughtful, patient, and rational, Agent Oberman seeks Violet's help as he attempts to solve Question Mark's latest mystery while also confronting his own personal challenges.
Alastair Applenight. CEO of New Tomorrow Industries, the tech-company responsible for digging the gigantic hole on the outskirts of town, Alastair Applenight is committed to building a particle collider that will forever alter the future of humankind and may even bring its end.
Dash Holland. High-schooler Dash Holland, son of police officer Dave Holland, assists customers at the Question Mark Video Store. With an interest in the occult and feeling slightly depressed since his twin brother began dating, Dash spends his free time drawing realistic sketches of celebrity deaths.
George Yakamoto. Father of Nanako, Dr. George Yakamoto is a researcher at the University of Ohio Extension Experimental Crop Station, who may or may not be hiding several secrets regarding surprising, frightening developments at the ECS.
Everard Bright. A professor at the University of Cincinnati in the Department of Apocalypse Studies with an emphasis on cult theory, Prof. Bright warns Violet of the arrival of the Order of the Arranger, a doomsday cult from California that believes a powerful creature is hiding somewhere in the Question Mark Woods.
Jock Reynolds. Retired person Jock Reynolds coordinates the highly dangerous Amateur Kite Fighting Club every Sunday at British Soldier Field while also serving as the lone member of the Question Mark Historical Society, which now oversees the Upside-Down House. Brusque, unapologetic, though often kindly, Jock proves to be a resource for any and all historical mysteries that may connect the town's many disappearances to the appearance of The Void.
Theophilus Willey. Amiable, earnest, though somewhat clumsy, Theophilus Willey is the great-great-nephew of town founder, Reginald Willey. At a young age, Theophilus studies his great-great-uncle's manuscripts and uncovers the mystery of The Void. After failing out of MIT and being excommunicated from his family, Theophilus struggles to save the town from impending doom, leaving Violet notes and clues, while hoping to prove to his family that he is worthy of the Willey name.
Tanner Pratt. Retired Navy lieutenant and possible time-traveler, Tanner Pratt is desperate to warn Violet and the rest of the town of Question Mark about an impending catastrophe that may involve the New Tomorrow Industries particle collider, the Order of the Arranger, or some other unknown calamity.