Reuel is a talented medical student in Boston who struggles financially and lives an isolated life. Though his olive skin often leads his peers to speculate about his origins, he quietly conceals his biracial identity to avoid racial prejudice. He possesses a strong interest in mysticism, mesmerism, and the supernatural, often experiencing profound visions that guide his actions and lead him to explore alternative medical treatments.

Dianthe is a gifted soprano who performs with a group of touring singers. Her captivating voice deeply moves audiences, expressing the profound sorrows and hopes of her people. After a severe train accident leaves her in a seemingly fatal coma, she suffers from total amnesia and becomes dependent on the care of the doctors and friends who take her in, temporarily going by the name Felice Adams.

Aubrey is a wealthy, white medical student from a prominent Southern family and Reuel's only close friend. He acts as a patron, helping Reuel financially through college while maintaining a somewhat superior demeanor. Engaged to Molly Vance, he soon develops an intense, obsessive interest in Dianthe after her accident and attempts to insert himself into her life.

Ai is the prime minister and a spiritual leader in the hidden ancient city of Telassar. He possesses deep knowledge of Ethiopian history and culture, along with genuine mystical abilities that connect him to the supernatural world. He serves as a guide for visitors to his hidden society, challenging Western rationalism with his profound spiritual insight.

Charlie is a wealthy, good-natured young white man who frequently hosts social gatherings at his family's suburban mansion. Seeking adventure rather than a quiet domestic life, he eagerly joins the medical and archaeological expedition to the ancient cities of Africa alongside Reuel.

Molly is Charlie's sister and Aubrey's fiancée. She is an innocent, welcoming woman who graciously opens her home to host Dianthe as a guest during the singer's long medical convalescence.

Jim is a Black attendant hired to accompany the expedition to Africa. He assists the men as they travel across the desert to Meroe, though his quiet presence during dangerous encounters eventually raises questions about his reliability.

Professor Stone is the leader of the expedition to the ancient Ethiopian capital of Meroe. He is a passionate theorist who strongly believes that ancient African civilizations are the true source of world art and science, eagerly seeking a fabled hidden city beneath the pyramids.

Mira is a formerly enslaved woman who belonged to Aubrey's father. She possessed renowned spiritual insight and once accurately predicted the widespread destruction of the Civil War. She frequently appears as a ghostly vision to both Reuel and Dianthe, carrying cryptic warnings about the past.

Aunt Hannah is an elderly woman who lives in a secluded cabin in the woods near the Livingston estate in Maryland. She serves as a keeper of history, holding onto the dark and painful memories of the local families from the era of enslavement.

Queen Candace is the virgin monarch of the hidden city of Telassar. She awaits the arrival of a prophesied king to help restore her civilization's former glory. She bears a striking physical resemblance to Dianthe.

Ababdis is a camel driver and guide who travels with the expedition across the Sahara. He maintains a watchful eye over the travelers while harboring his own ties to the local indigenous populations.