Nizhoni is a seventh-grade Navajo student who recently transferred to an intertribal charter school in Albuquerque. Following her coming-of-age ceremony, she develops the instinctual ability to detect supernatural monsters disguising themselves as humans. She struggles with feelings of abandonment because her mother left the family years ago, while also trying to protect her younger brother. Her discovery of her abilities initiates a desperate quest to seek ancient weapons and stop a corporate villain.

Marcus, commonly called Mac, is Nizhoni's younger brother, separated in age by only ten months. He is an artistic student who saves his allowance for drawing supplies. Initially skeptical of his sister's monster-hunting claims, Mac soon discovers he possesses latent water-manipulation abilities. He brings humor and occasional complaints to their difficult journey.

Davery is Nizhoni's academically driven best friend and a dedicated student at their middle school. He founds the Ancestor Club to encourage students to present their heritage and family lineages. When Nizhoni confides in him about monsters, Davery immediately believes her and uses his research skills to support her mission.

Mr. Yazzie is Nizhoni’s stuffed horned toad toy, purchased from a museum gift shop, who magically comes to life. He speaks both English and Navajo. Serving as a connection to the Holy People, he informs the children of their heritage as descendants of the Changing Woman and sets them on their path to the House of the Sun.

Mr. Charles is the wealthy potential employer of Nizhoni’s father and the CEO of Landrush Oil and Gas. He is secretly a bináá’yee aghání, an ancient shapeshifting bird monster. He intends to exploit Native American lands for a pipeline while kidnapping individuals with latent supernatural abilities.

Mr. Begay is Nizhoni and Mac’s father, a single parent striving to provide for his family financially. He is highly focused on securing a lucrative position with Landrush Oil and Gas, making him emotionally distant and blind to the dangers surrounding his children. His focus on career advancement causes him to dismiss Nizhoni's warnings about his new boss.

Bethany is Nizhoni and Mac’s mother, who abandoned the family when the children were toddlers. She also possessed the ability to see monsters. Her sudden departure left a lasting wound on her family, though Nizhoni soon learns she left to hunt the very creatures now threatening her children.

Na’ashjéii Asdzáá, or Spider Woman, is a Navajo Holy Person residing in a mobile home. She appears as an expert rug weaver and offers the children essential guidance for their journey. She requires gifts of sacrifice from the sacred mountains before showing them the path forward.

Jóhonaa’éí, also known as the Merciless One or the Sun, is a powerful Holy Person who resides in the House of the Sun. He possesses the ability to forge lightning into specialized weapons for those brave enough to complete the trials of the Rainbow Road.

Black Jet Girl is the guardian of Dibé Nitsaa, the sacred Mountain of the Folding Darkness. She is made entirely of black rock. After falling victim to the paralyzing gaze of bird monsters, she relies on outside intervention to secure her mountain.

Łizhin is the herald of Dibé Nitsaa, appearing as a massive bird. She transports heroes across the region and offers cryptic but crucial advice about trusting one's instincts in the face of danger.

Rock Crystal Boy, or RC, is the guardian of Sisnaajiní, the sacred eastern mountain. Made entirely of white crystal, he honors traditional Navajo introductions and clan relationships, granting access to his mountain's resources to those who respect customary greetings.

Shimásání is Nizhoni's maternal grandmother. She taught Nizhoni traditional Navajo customs and proper clan introductions. She cares deeply for her family and views her relationship with her dogs as a communal partnership rather than ownership.

Adrien Cuttlebush is a middle school student who relentlessly bullies Mac. He uses hateful rhetoric to mock other students and travels with a group of friends who support his cruelty.

Ms. Bird is one of Mr. Charles's bodyguards. She projects an intimidating physical presence and assists in her employer's sinister corporate and supernatural activities.

Mr. Rock acts as a bodyguard for Mr. Charles. Alongside Ms. Bird, he provides muscle for Landrush Oil and Gas, helping suppress dissent and capture targets for his boss.