Hiram is a young enslaved man at Lockless Plantation who possesses a perfect memory, except for the day his mother was sold away. Gifted with extraordinary intelligence and a supernatural ability to bend space and time called Conduction, he works as a manservant to his half-brother. He struggles to reconcile his desire for freedom with his complicated ties to his white father and the enslaved community he loves.

Sophia is an enslaved woman who desires autonomy and freedom above all else. After her original mistress dies, she is forced to become the concubine of Nathaniel Walker. She is deeply pragmatic, prioritizing her own survival and independence over romantic idealism.

Corrine is a wealthy white woman of the Quality who leads a double life as a ruthless operative in the Underground. Outwardly playing the role of a Southern belle, she secretly dedicates her resources to dismantling slavery. She approaches her anti-slavery work with a cold pragmatism that often puts her at odds with others.

The master of Lockless Plantation and the biological father of both Hiram and Maynard. Howell views himself as a benevolent patriarch but embodies the deep hypocrisy of the slaveholding class. He readily sells away the families of his enslaved workforce to cover his mounting financial debts.

A legendary figure in the Underground who possesses the supernatural power of Conduction. She uses memories and the emotional power of storytelling to transport enslaved people to freedom. She operates with strict rules and maintains absolute secrecy to protect her rescue missions.

An agent of the Underground who maintains a careful double life. Under the alias Mr. Fields, he poses as a subservient tutor to the Virginia elite. In secret, he works as a dedicated operative who conducts field missions to steal enslaved people away from their masters.

Hiram’s mother and a beautiful woman known for her skill in traditional water dancing. Howell sold her away from Lockless when Hiram was just a boy, leaving a traumatic gap in her son's otherwise perfect memory.

Howell's brother and Hiram’s uncle. Nathaniel is a wealthy slave owner who spends much of his time out in Tennessee. He leverages his power over the enslaved women he owns, claiming Sophia as his concubine while maintaining a public facade of Southern gentility.

An agent of the Philadelphia station of the Underground. Otha carries deep emotional wounds from being left behind in slavery as a child when his mother escaped. He models a tender, respectful masculinity while hoping to reunite with his enslaved wife in Alabama.

A formerly enslaved man who managed to gain his freedom and establish a seemingly prosperous life in town. Rumored to have connections to the Underground, he is approached by Hiram for help escaping Lockless.

Hiram's grandmother, a native-born African woman possessing the power of Conduction. According to local lore, she used her supernatural abilities to walk forty-eight enslaved people into the Goose River and return them to Africa.

Howell’s legitimate white heir and Hiram’s half-brother. Maynard is a crude gambler whom the local gentry despise. He relies entirely on Hiram's competence to function in daily life, embodying the moral decay of his class.

An enslaved woman at Lockless known for her moodiness and anger, stemming from the trauma of losing her entire family. She raises Hiram and fiercely warns him about the dangers of trusting the white masters.

Corrine Quinn's manservant who is deeply involved in the Underground. He works on terms of startling equality with Corrine behind closed doors and assists in orienting new agents to the organization's methods.

A Black agent of the Underground who helps manage operations in Philadelphia alongside his brother. He coordinates rescue missions and secures forged documents for those seeking freedom.

Thena’s daughter, who formerly watched over Hiram when he was a baby. After being sold away by Howell, she managed to gain her freedom by marrying into Moses's family.

Otha's wife, who survives enslavement in the Deep South. She shares a deep bond with her husband and focuses intensely on survival over pride, helping Otha navigate the emotional toll of their bondage.

A field agent for the Underground who operates in Virginia. She helps orient Hiram to the complex structure of the organization, distinguishing between the intelligence-gathering house agents and frontline field agents.

Caroline is Sophia’s young daughter, born as a result of Sophia's forced relationship with Nathaniel Walker. She possesses the typical green-gray Walker eyes, clearly marking her parentage. Her presence becomes a central reason for her mother's cautious, pragmatic choices regarding escape.