Edgar is a young man living with his uncle in rural Pennsylvania in 1787. Tormented by the recent murder of his fiancée's brother, he becomes obsessive in his search for the killer. His investigations lead him to observe the strange nocturnal habits of a local immigrant servant. He is prone to sleepwalking, a trait he shares with his primary suspect, and possesses a restless disposition that drives him to explore the uncultivated wilderness surrounding his home.

Clithero is an Irish immigrant who works as a servant for Mr. Inglefield. He is the only foreigner among the Anglo-Saxon settlers in his area, making him a subject of quiet suspicion. Diligent during the day, he exhibits mysterious and distressing sleepwalking behavior at night, driven by repressed trauma from his past life working for a wealthy family in Ireland.

Though inexplicably listed under the heading "Mrs. Sarsefield" in analytical study notes, Sarsefield is a male surgeon and Edgar's former tutor who has spent time traveling through Europe, the Middle East, and Asia. Educated and refined, he represents a civilized contrast to the wild American environment. He maintains strong ties to Euphemia Lorimer in Dublin and acts as a stabilizing, parental figure for Edgar.

Euphemia is a wealthy and cheerful widow living in Dublin, Ireland. She is known for her extreme benevolence, frequently taking in dependents and providing financial support to those in need, including her servants and former suitors. She acts as a foster mother to her niece and maintains a deep loyalty to her family despite their flaws.

Arthur is Euphemia Lorimer's twin brother, possessing a nature completely opposite to hers. He is a depraved and violent criminal whose actions actively sabotaged his sister's early happiness. Banished and presumed dead during a mutiny on a felon ship, his destructive legacy continues to haunt those connected to the Lorimer family.

Clarice is the daughter of Arthur Wiatte, raised as a foster child by her aunt Euphemia Lorimer after her father's supposed death. She bears a striking physical resemblance to Euphemia and develops a close bond with Clithero, whom she is raised alongside in the Lorimer household.

Mary is Edgar Huntly's fiancée and the sister of the recently murdered Mr. Waldegrave. She serves as the silent audience for Edgar's lengthy epistolary confession. Dependent on her brother's mysterious inheritance for her future marriage, she remains a distant but motivating presence throughout Edgar's investigation.

Mr. Waldegrave is Mary's brother whose murder near an elm tree initiates Edgar's quest for justice. Before his death, he worked as a teacher at a school for free Black Americans and privately held unorthodox, anti-religious beliefs which he later renounced. He left behind a substantial sum of money of mysterious origin.

Mr. Inglefield is a steadfast and kind neighbor to the Huntly family in rural Solesbury. He acts as a sounding board for Edgar's theories and provides a stable presence in the community. He employs the Irish immigrant Clithero and treats Edgar with paternal affection.

Mr. Huntly is Edgar's uncle and guardian, having taken the young man in after his parents were murdered in a previous conflict. A retired military man, he provides Edgar with a home in Solesbury and previously hired Sarsefield to oversee his nephew's education.

Mr. Weymouth is a traveling merchant who lost everything in a shipwreck. He tracks down Edgar to claim that the large sum of money left behind by the late Mr. Waldegrave actually belongs to him, threatening Edgar and Mary's financial future.

Old Deb, nicknamed Queen Mab by Edgar, is an elderly Leni Lenape woman who chose to stay behind in Norwalk when her tribe migrated west. She lives in an isolated hut with three intimidating wolf dogs, speaking incessantly to them and maintaining her traditional way of life on the fringes of the white settlement.

Ambrose is a servant working at Mr. Inglefield's estate. As Clithero's roommate, he observes the Irish immigrant's restless nights and sleep-talking, providing crucial corroborating details to Edgar regarding Clithero's strange habits.

Old Gowan serves as a porter at Euphemia Lorimer's estate in Dublin. He stands watch at her gate and interacts with unwanted visitors, fulfilling his duties to protect the household from threats.