Lady Susan is a highly attractive, thirty-five-year-old widow who utilizes her exceptional conversational skills to charm the people around her. Having recently sold off her late husband's family estate to maintain her luxurious lifestyle, she actively seeks new, financially advantageous marriages for both herself and her teenage daughter. She prioritizes wealth and personal freedom over conventional morality, operating strategically in a society that expects women to remain passive and sincere.

Catherine is the socially proper, highly observant wife of Charles Vernon. She accurately assesses Lady Susan's deceptive nature early on and deeply resents her presence, carrying a grudge because Susan previously tried to block Catherine's marriage to Charles. Seeking to protect her family's reputation from scandal, Catherine attempts to counter her sister-in-law's machinations while simultaneously stepping in to act as a proper maternal figure to her neglected niece.

Frederica is Lady Susan's sixteen-year-old daughter. Timid, submissive, and reportedly uneducated, she stands in sharp contrast to her confident mother. She actively resists being forced into an arranged marriage with a man she openly despises, eventually fleeing her school to seek refuge and assistance from the kinder adults at the Churchill estate.

Reginald is Catherine's younger brother, a handsome man who prides himself on his intelligence and analytical nature. Despite arriving at Churchill with a strong prejudice against Lady Susan based on rumors of her behavior, he quickly falls under her spell. He naively believes he understands her true motives better than anyone else, leading him to dismiss the frantic warnings of his own family.

Alicia is Lady Susan's most trusted friend and a willing accomplice in her social maneuvering. Tied to an older, ailing husband she actively dislikes, Alicia lives vicariously through her friend's independent exploits. She assists Susan by passing along letters, providing a cover story, and offering strategic advice on how to handle various suitors.

Charles is the wealthy, pleasant brother of Lady Susan's late husband. He prefers a quiet country life away from London society and generally avoids taking sides in the domestic conflicts happening under his roof. He remains somewhat oblivious to the deeper manipulations occurring around him, choosing to see the best in his grieving sister-in-law.

Sir James is an extremely wealthy bachelor. He is easily swayed by Lady Susan to abandon his previous romantic interest and pursue her young daughter instead. He lacks basic social awareness and frequently shows up uninvited, acting as a disruptive force to the plans of everyone around him.

Mr. Manwaring is a married man who becomes deeply and visibly infatuated with Lady Susan during her extended visit to his estate. He represents the kind of blatant adoration Susan enjoys, though his existing marriage complicates any permanent arrangement they might pursue.

Mrs. Manwaring is Mr. Johnson's former ward and the deeply unhappy wife of Mr. Manwaring. She suffers greatly from the chaos Lady Susan introduces into her household and actively seeks outside intervention to save her marriage and remove her rival.

Mr. Johnson is Alicia's older, gout-ridden husband who accurately perceives Lady Susan as a terrible influence. He uses his authority as a husband to restrict his wife's movements and friendships, demonstrating the strict societal control men maintain over women in this era.

Sir De Courcy is Reginald and Catherine's father, an older gentleman highly concerned with the preservation of his family's respectable name. He views any association with Lady Susan as a direct threat to his lineage and attempts to use his paternal authority to force his son to return home.

Lady De Courcy is Catherine and Reginald's mother. She shares her daughter's intense anxieties regarding Reginald's safety from Lady Susan's influence, but finds her ability to intervene limited when her husband takes control of their family correspondence.