Thomasina is a 13-year-old student living at the Coverly estate in Derbyshire during the early 19th century. She possesses extraordinary mathematical ability and an insatiable curiosity about both algebraic equations and the adult world. She questions traditional ways of thinking, demonstrating a mind far ahead of her time.

Septimus is a 22-year-old Cambridge-educated tutor working at the Coverly estate in 1809. He balances his teaching duties with secret romantic affairs and witty social maneuvering. He attempts to protect his academic interests while avoiding the consequences of his romantic indiscretions with other guests at the estate.

Hannah is an academic researcher and writer visiting the Coverly estate in the present day to study its historical garden renovations and the property's mysterious hermit. She maintains a rational, skeptical approach to history and rejects the emotional excesses associated with the Romantic era. She is deeply committed to finding concrete proof for her historical theories.

Bernard is a confident university academic visiting the estate to research Lord Byron. Driven by a desire for fame and recognition, he relies heavily on his intuition and eagerly jumps to conclusions to support his theories. He frequently clashes with other scholars over his methodology and arrogant demeanor.

Valentine is a graduate student at Oxford studying mathematics and biology who currently resides at his ancestral family estate. He uses computers to analyze historical game book data to find population algorithms. He serves as a bridge between the mathematical theories formulated in the past and their modern applications.

Lady Croom is the formidable, sharp-tongued matriarch of the Coverly family in 1809. She holds strong opinions about aesthetics, education, and the behavior of her guests. She strongly prefers order and classical beauty over modern, untamed styles.

Chloe is a modern-day descendant of the Coverly family living at the historic estate. She observes the academics working in her home and takes a strong, immediate interest in their personal lives and romantic entanglements.

Gus is the youngest modern-day sibling of the Coverly family. He never speaks during the events at the estate but frequently interacts with the visiting academics by offering small gifts and running errands.

Captain Brice is a naval officer and guest at the Coverly estate in 1809. He acts as a traditional gentleman and frequently inserts himself into disputes among the other guests, attempting to maintain order and proper conduct.

Ezra Chater is an unsuccessful poet staying at the Coverly estate in 1809. He is easily manipulated by flattery regarding his writing, which often blinds him to the reality of his domestic situation and his wife's indiscretions.

Richard Noakes is a landscaper hired to remodel the Coverly estate gardens in 1809. He aims to update the property to fit current aesthetic trends, favoring wild, irregular designs over orderly, classical ones.

Lord Augustus is the young son of the Coverly family in 1809. He frequently causes minor disruptions around the estate and looks for opportunities to get his older sister in trouble with their parents.

Jellaby is the butler at the Coverly estate in 1809. He is well-informed about the household's secret affairs and discreetly passes information and messages between the residents.