Casiopea is an 18-year-old woman living in her grandfather's oppressive household in 1920s Mexico. Relegated to the status of a servant because her mother had a child out of wedlock, she spends her days shining boots and dreaming of freedom. Curious and quietly defiant, her mundane life fractures when she opens a forbidden chest in her grandfather's room, unknowingly binding herself to an ancient god.

Hun-Kamé is the Supreme Lord of Xibalba, the Mayan Underworld, and the rightful god of death. Trapped in a wooden chest for fifty years by his treacherous brother, he seeks to recover his missing body parts—an eye, an ear, and a finger—to reclaim his godhood. Because a bone shard is embedded in Casiopea's hand, he relies entirely on her mortal life force to sustain his presence on Earth.

Vucub-Kamé is Hun-Kamé's twin brother and the self-appointed ruler of Xibalba. Having lived in his brother's shadow, he wishes to return the human world to ancient times when mortals worshipped the gods through brutal blood sacrifices. He uses dark magic, prophecies read in animal blood, and mortal pawns to maintain his stolen throne.

Martín is Casiopea's cousin and the favored grandson in the Leyva household. He masks his deep-seated insecurities and fear of the wider world with arrogance, bullying those he considers beneath him. When the gods' conflict spills into the mortal world, he is recruited as a champion for the Underworld's current ruler.

Cirilo is Casiopea and Martín's grandfather, a cruel patriarch who rules his family with strict, unyielding authority. Fifty years prior, as a poor man desperate for status, he made a dark bargain with an immortal being, acting as the bait to trap a god in exchange for wealth and societal influence in his hometown.

Loray is a demon known as the Marquis of Arrows who has integrated into the high society of Mérida. Outwardly appearing as a refined gentleman with impossible green eyes, he operates strictly on self-interest, offering aid, transportation, and information based solely on who he believes holds the current advantage in the godly war.

Xtabay is a seductress spirit from Mayan mythology who has relocated from her traditional forest home to enjoy the modern luxuries of Mexico City. Guarding a crucial piece of godly essence, she uses her supernatural charms to manipulate men and bargain for a higher position in the Underworld hierarchy.

Aníbal is a skilled mortal sorcerer working in devoted service to the current ruler of Xibalba. Stationed in Baja California, he acts as an instructor and guide, teaching dark magic and explaining the deadly mechanics of the Underworld to those recruited into his master's service.

Casiopea's mother lives as little more than a servant in her father's house after having a child out of wedlock with a man her father disapproved of. Beaten down by her circumstances and strict patriarchal rules, she encourages her daughter to keep her head down and accept their lot in life without complaint.

The youngest of the Mamlab, a group of Huaxtec Mayan weather gods, he controls thunder and is highly mischievous. Disguising himself during the vibrant Carnival in Veracruz, he holds a stolen piece of godly essence and relies on mortals' changing beliefs to maintain his existence.

The Uay Chivo is a sorcerer and half-beast from regional folklore who resides in El Paso, Texas. Capable of transforming into a giant fire-breathing goat, he guards a stolen jade necklace and relies on fiery magical traps to slow down anyone attempting to retrieve the artifact.