Opal is a twenty-six-year-old woman living in the small town of Eden, Kentucky, at the run-down Garden of Eden Motel. She struggles financially to provide for herself and her younger brother. She dreams of a better life far from their prejudiced community. Fiercely independent, she views relationships as transactional and avoids asking for help. She accepts a job as a housekeeper at the mysterious Starling House to pay for her brother's asthma medication and private schooling.

Arthur is the twenty-eight-year-old reclusive owner of the infamous Starling House. He lives in isolation, burdened by the dark legacy of his family and the property he oversees. He acts curt and unwelcoming to outsiders but surprisingly hires Opal as his housekeeper. He spends much of his time researching mysterious beasts and practicing swordsmanship.

Jasper is Opal's bright sixteen-year-old brother who suffers from asthma. He excels academically and possesses a strong creative streak, often spending his free time producing artistic videos. He faces microaggressions in the predominantly white town of Eden due to his Latino heritage. He resents his sister's overbearing need to control his future and desires the freedom to make his own choices.

Eleanor is the legendary first resident of Starling House and the subject of Eden's darkest local rumors. She wrote a children's book called The Underland, which tells the story of a girl hiding from a fox. Town gossip claims she murdered her husband and his two brothers shortly after her wedding. Her legacy casts a long shadow over both the house and the town's history.

Jewell is Opal and Jasper's late mother. She lived a chaotic life built on favors, charity, and transient relationships, frequently inventing new last names for her family. Her death in the Mud River left Opal with severe survivor's guilt and the sole responsibility of raising Jasper.

Elizabeth is a polished corporate representative working for Gravely Power. She tasks herself with researching anomalous events connected to Starling House. She uses coercion and veiled threats to force Opal into spying on Arthur and taking photographs of the property's interior.

Bev owns the run-down Garden of Eden Motel where Opal and Jasper live. She allows the siblings to stay for free due to a mysterious past arrangement with their mother. Despite her gruff exterior and frequent arguments with Opal, she acts as a subtle support system for the siblings.

Charlotte is the local librarian in Eden who actively researches the town's history. She provides Opal with access to old documents and recordings that contradict the widely accepted stories about the Gravely and Starling families. She serves as a gentle, grounding presence in Opal's chaotic life.

Don Gravely is the wealthy owner of Gravely Power, the primary economic force in Eden. His family has controlled the town's wealth and narratives for generations. He lives in a large estate outside the city limits and directs efforts to expand his company's reach across the region.

Calliope is a Black woman whose family maintains an alternative history of Eden. She recorded an oral history for the library that details the brutal realities of the Gravely family's past and their use of enslaved labor, challenging the sanitized local lore.

Nathaniel is a historical figure in Eden who was enslaved by the original Gravely brothers to work in their coal mines. According to alternative town lore, he discovered mysterious cracks deep within the earth and warned Eleanor Starling about what lay beneath the town.

John Gravely is a historical figure from Eden's past, remembered as one of three wealthy brothers who founded the town's coal empire. According to local legend, he briefly married Eleanor Starling before he suffered a sudden, violent death that the town blames on his new bride.

Constable Mayhew is a local law enforcement officer in Eden. He aligns himself with the powerful interests in town, specifically Gravely Power, and has a history of interpreting the law in ways that benefit the town's elite while disregarding marginalized citizens.

Baast is a stray cat that Opal rescues from the Garden of Eden Motel and brings to Starling House. Opal nicknames the animal "the hellcat" due to its abrasive temperament. The cat slowly integrates into the strange environment of the house.

Lacey is Opal's coworker at the local Tractor Supply store. She represents the general populace of Eden; she readily believes and shares the town's sensational rumors about Starling House and its supposed satanic rituals.