Eloisa is an eighteen-year-old, highly gifted student who begins a passionate, clandestine affair with her much older tutor. After the relationship creates a severe scandal leading to violent retaliation from her family, she is forced to live as a nun in a convent. She writes a long, desperate letter to her former lover, struggling to choose between religious devotion and her enduring romantic passion. She openly prefers emotional freedom and intellectual connection over conventional societal rules like marriage.

Abelard is a renowned thirty-eight-year-old philosopher, theologian, and poet in medieval Paris. He initially secures a room in a local home to serve as a tutor for a brilliant young student, eventually beginning a secret romantic relationship with her. Following a violent attack orchestrated by the girl's family, he retreats to live in a monastery, leaving his lover with only memories and written correspondence.

Canon Fulbert is a prominent member of the clergy at Notre Dame Cathedral in Paris and serves as Eloisa's guardian. He initially welcomes Abelard into his home as a tutor, entirely unaware of the developing romance occurring under his roof. When he discovers the scandalous relationship and subsequent secret marriage, he takes drastic, violent measures to punish the man he views as ruining his niece.

Astrolabe is the infant child of Eloisa and Abelard, uniquely named after an astronomical instrument used to measure the distance of stars. Because of the massive scandal surrounding his parents' relationship and their mutual retreat into isolated religious orders, he is sent away to be raised by his aunt.

She is the unnamed sister of the scholar Abelard. When public scandal forces her brother and his young lover to separate into different religious orders, she takes responsibility for raising their infant child, Astrolabe, keeping the boy away from the fallout in Paris.