The 12-year-old eldest Greystone sibling. Following the death of his father eight years ago, Chess feels an overwhelming burden to protect and care for his younger siblings. He is highly sensitive and struggles with anxiety, frequently wishing he had an adult to rely on when circumstances turn dangerous and confusing. He often tries to act older than his age but is secretly intimidated by the unfolding mysteries.

The 10-year-old middle Greystone child. Emma is exceptionally analytical. She possesses a deep love for math and secret codes. She relies on the predictability of facts and equations to ground herself when she feels stressed. The sudden and irrational nature of her mother's disappearance is particularly difficult for her to process, forcing her to accept things that cannot be solved with a simple formula.

The eight-year-old youngest Greystone sibling. Impetuous and fiercely attached to his mother, Finn treats much of life as a grand adventure. Because he does not remember his father and is used to being protected by his older siblings, he approaches the mystery with a youthful, outside-the-box imagination that yields unexpected clues.

A website designer and the devoted single mother of Chess, Emma, and Finn. She is usually warm and highly organized, leaving detailed itineraries for her children. When she departs on a sudden "business trip" after watching a disturbing news broadcast, she leaves behind a trail of hidden clues, panic rooms, and secrets about her true origins.

Ms. Morales's 13-year-old daughter. Initially appearing as a sullen, bored teenager who resents her mother's authority, Natalie proves observant and surprisingly invested in the Greystones' well-being. She uses her smartphone, her confident demeanor, and her social awareness to actively assist the siblings in their investigation.

An authoritarian judge encountered during the kids' investigation into their mother's past. She is identical in appearance to Natalie's mother, Ms. Morales, but serves as a stern enforcer of state doctrine, using fear and propaganda to manipulate citizens in a deeply repressive society.

A real estate agent and private investigator who steps in as a babysitter when Kate Greystone abruptly leaves town. She is a single mother dealing with a recent divorce, trying to balance her demanding jobs with managing her rebellious teenage daughter. She maintains a cautious, overly cheerful facade that makes the children wary.

A mysterious man who corresponds with Kate Greystone regarding a dangerous, hidden situation. He possesses significant technical skills and utilizes a hand-drawn crooked heart symbol to identify himself to allies. He knows far more about the strange occurrences surrounding the Greystone family than he initially reveals.

The deceased husband of Kate and father to Chess, Emma, and Finn. His death deeply impacted the family, particularly Chess, who feels pressured to fill his shoes. Questions about his past arise as the children investigate their mother's sudden disappearance.

One of three kidnapped children from Arizona who share identical first and middle names, as well as exact birth dates, with the Greystone siblings. His high-profile disappearance sets the entire mystery in motion for the Greystone family.

A kidnapped child from Arizona who inexplicably shares a name and birthday with Emma Greystone. Her abduction distresses the Greystones, who desperately search for logical explanations for the bizarre coincidences.

The youngest of the abducted Gustano children. Like his siblings, he shares his exact name and date of birth with his Greystone counterpart, raising alarming questions about identity and hidden familial connections.

The mother of the kidnapped Gustano kids in Arizona. The Greystone children are completely shocked to discover she bears a near-identical physical resemblance to their own mother, adding to the growing mystery of their family's true origins.

The father of the kidnapped Gustano children. Unlike his wife, who closely resembles Kate Greystone, Arthur does not physically resemble the late Andrew Greystone, confusing the kids' theories about twin families.

Finn's school classmate who claims to have seen Kate Greystone running out of a bank carrying a bag on the day she disappeared. He eagerly speculates that she is a bank robber making a getaway, which deeply unsettles Finn.