Clara is an intelligent, independent young woman who lives alone on her inherited half of the Mettingen estate. Unlike her brother, she holds a relaxed, nature-based approach to religion, though she frequently struggles to distinguish between objective reality and the supernatural. She is susceptible to romantic ideals and deeply values the isolated, idyllic community she shares with her brother and friends.

Francis Carwin is a mysterious stranger who arrives in the pastoral community of Mettingen. He presents a striking physical contradiction, possessing an ungainly, stooped appearance that contrasts sharply with his highly educated voice and polished manners. He initially approaches Clara's home asking for a cup of water, quickly becoming a disruptive, trickster-like presence in the family's once-tranquil lives.

Theodore is Clara's brother and Catherine's devoted husband. He inherited his father's sober, thoughtful disposition and a tendency toward deep, uncompromising religious contemplation. While he strongly values his role as a loving caretaker for his family, he increasingly fixates on spiritual transcendence, eagerly searching for a direct, undeniable connection with God.

Henry Pleyel is Catherine's brother and a close friend of the Wieland family. He considers himself a strict rationalist, preferring to rely on intellect and logic rather than historical authority or religious tradition. Boisterous and highly opinionated, he views Clara as a model of ideal womanhood but remains entirely oblivious to her romantic infatuation with him.

Catherine is Theodore's wife, Clara's childhood friend, and Henry's sister. She lives in the main Wieland house with Theodore and their children, providing a grounded, stabilizing presence. She frequently participates in the evening gatherings at the estate's temple, enjoying the idyllic, isolated community before strange events begin to unfold.

Wieland Sr. is the deceased patriarch who originally established the Mettingen estate. He was a deeply disciplined man prone to severe depression and religious fanaticism, adhering to a highly idiosyncratic, self-invented form of Protestantism. His sudden, inexplicable death by apparent spontaneous combustion while praying haunts his children and sets the stage for the family's ongoing tension between reason and faith.

Thomas Cambridge is the maternal uncle of Clara and Theodore Wieland. He is a physician and former army doctor who returned from living in Ireland. He provides a highly pragmatic, medical perspective on the family's history, frequently attempting to ground Clara with scientific rather than supernatural explanations.

Mrs. Baynton is a hospitable friend of the Wieland family who lives in Philadelphia. Her home serves as a convenient stopping point for members of the Mettingen community when they travel to the city for business, news, or socializing.

Louisa Conway-Stuart is the fourteen-year-old adoptive daughter of Theodore and Catherine Wieland. Her biological mother fled London with her when she was an infant, and Louisa was raised by Clara and Theodore's aunt before officially joining the Wieland household. She is cherished by the entire family for her sweet disposition.

Major Stuart is Louisa's biological father. He travels the country conducting personal business and unexpectedly reunites with his long-lost daughter. He leaves her in the care of the Wielands while he finishes his travels, keeping in touch through regular correspondence.

Maxwell is a rival from Major Stuart's past. He deliberately spread damaging rumors about Stuart that led to a violent duel, creating the initial fracture that ultimately caused Major Stuart's wife to flee with their infant daughter.

Theresa de Stolberg is a baroness living in Germany. She is the object of Henry Pleyel's intense affections, and her distant presence strongly influences his desire to abandon America and return to Europe.

Judith is Clara's maid, living and working independently at Clara's house on the Mettingen estate. She becomes involved with Francis Carwin, using the hollow in the riverbank for their clandestine meetings.