As the eldest of the Greystone children at age 12, and the only one with any tangible memories of their deceased father, Chess assumes the sobering responsibility of caretaker for his younger siblings. When their mother disappears and he, Emma, and Finn are plunged into danger, he feels, rightly or wrongly, that he must take up the adult mantle and protect them. Unfortunately, the bizarre circumstances and nearly insurmountable obstacles are too much for him, as they would be for any 12-year-old. Chess is torn between being a kid and being the eldest kid, a conflict that robs him of self-confidence when he needs it most. Up until now, he spent his life as the dutiful son, trying to fill his father’s shoes and to protect his mother from her own grief.

As a result, he is ill-prepared to handle the demands of coded letters and mysterious worlds. Chess is further hampered by encroaching puberty, which is especially troublesome when in the presence of Natalie. He finds her popularity intimidating, and he frequently stumbles over his words when he’s around her, although part of his character arc is overcoming his shyness and learning to respond to Natalie with confidence. In a sense, Chess is too old to effectively handle the crisis, and he must rely on his younger siblings to pull him back in time a few years, to the days when he could see the possibilities in the world and not just the limitations. 

Emma Greystone, age ten, sees the world through numbers and logic. As far as she is concerned, there is no problem that can’t be solved rationally. When she is bored at school, she entertains herself by looking for irregularities in her routine, mentally counting and cataloguing them. Emma’s logical mind serves her well in the search for her mother. Once she discovers the key, she is able to decode at least part of the letter. Further, when Finn notices that the dot patterns in various iterations of Kate’s business logo aren’t random, Emma figures out how to make sense of them. However, her insistence on rational explanations also works against her. When events take an otherworldly turn, Emma becomes paralyzed by doubt. While Finn is able to embrace the strangeness and accept it as real, that leap of faith does not come so easily to Emma. In the end, however, she does accept their illogical circumstances, primarily because her five senses leave her no other choice.

The youngest Greystone, eight-year-old Finn is impetuous, adventurous, and driven by his bond with his mother. Chess and Emma sometimes see him as Kate’s favorite, and perhaps they’re right. In the absence of their father, Kate feels a special responsibility toward her youngest child, and she tends to indulge him. With two older siblings to rely on, Finn is accustomed to being protected and, to some extent, coddled. His inclination to see the world as one big adventure can mean trouble, especially when it’s not accompanied by enough impulse control. When he proclaims his mother’s innocence in the middle of a largely hostile crowd, it nearly ruins their rescue efforts.

As he and his sibling use smoke bombs to distract the guards in the auditorium, he fails to understand the stakes involved, seeing it as just a game. Finn will charge ahead into unknown territory before the others because his youth prevents him from imagining an unsafe world that may want to harm him. His youthful spontaneity is an asset at times, though. His ability to think outside the box is exactly what’s needed when dealing with something as surreal as an alternate world. He is the one who initially notices the patterns in the butterfly dots. He is the one who pushes the others onward when all seems lost. As the youngest, he is also the one who feels his mother’s absence the most acutely, and this yearning keeps him going when logic would dictate giving up. 

Since the novel is told through the eyes of the children, Kate Greystone is something of an enigma. Through Finn’s eyes, she is the fun mom, always ready with hugs and cookies. To Emma, she is the mom who nurtures her daughter’s passion for math, suggesting books on codes and codebreaking. To Chess, she is the single mother who needs his emotional support. As Haddix reveals further into the novel, however, Kate is also a revolutionary, a political dissident working to overthrow a repressive regime. She is a woman of supreme conscience or foolhardiness, depending on how you look at it. Kate is willing to leave her children and risk her own life to save the Gustanos, who are strangers to her and in danger because of her actions. Ultimately, she is a loving mother who is torn between the welfare of her own family and atonement for her past deeds. Whether or not she hopes to overthrow the government in the alternate world and bring her family back is unclear, but the desire to make the world—any world—a better place for future generations is an aspiration most parents can identify with.

Natalie is the 13-year-old daughter of Susanna Morales, the woman tasked with taking care of the Greystone children while their mother is away. At first glance, Natalie appears to be little more than a stock character—the sullen, defiant teenager who argues with her mother over every perceived transgression. She rarely lifts her eyes from her phone, barely acknowledging the Greystones’s presence until her mother orders her to keep an eye on Finn, which she does reluctantly. Slowly, however, Natalie becomes intrigued by the mystery of Kate’s disappearance, and over time, she becomes a valuable ally. Haddix provides little reason for Natalie’s sudden interest other than boredom. Consequently, her motivations are suspicious to Chess, Emma, Finn, and the reader.

Natalie is also referred to by Chess as a former “Lip Gloss Girl,” a member of an exclusive clique of popular girls who dominated the school yard before moving on to middle school. As with the other kids, Natalie possesses certain personality traits that come in handy in a crisis—in this case, her steely-eyed confidence as a popular kid. When called upon to play the part of Judge Morales’ daughter, a girl with power and status, she does so almost too easily, ordering guards to let her pass with the Greystone and Gustano children and even improvising when the guards hesitate. Natalie offers her assistance without any personal stake in the matter. By the end, however, with her mother trapped in the other world, she has just as much to lose as Chess, Emma, and Finn do.

Like Kate Greystone, or any adult in the novel, Ms. Morales is a thinly sketched character, only seen through the eyes of the children. She is primarily defined by her relationship with Natalie, and as such she comes across as the beleaguered single mother, trying to juggle two jobs and a rebellious teenage daughter. Haddix, though, provides glimpses of Morales’s love and humanity now and then. She consoles Finn when he’s upset and even entrusts Natalie with some responsibility despite her reservations. She understands that much of Natalie’s anger is a result of her divorce, and so she tries to empathize with her daughter; but even the most patient parent can be tested by a grumpy, seemingly ungrateful child. In the alternate universe, Judge Susanna Morales is a stern enforcer of state doctrine, playing the crowd like a violin and whipping them into a nationalistic frenzy. She is a feared figure in her world, and while it’s tempting to view the two Susanna Moraleses as two halves of the same personality, Haddix doesn’t delve into psychological complexities here. She is content to let her characters serve her narrative purpose by keeping the action moving.