Susan is a seventeen-year-old orphan who lives in a bustling Lant Street household of thieves. She operates as a "fingersmith" under the protection of her surrogate mother. Though street-smart and resourceful, she lacks formal education and cannot read or write. She agrees to pose as a lady's maid to help swindle a wealthy heiress.

Maud is a wealthy orphan raised in strict isolation at Briar, a gloomy country estate. She serves as a captive secretary to her domineering uncle, cataloging his massive, controversial collection of literature. Despite her extensive reading, she remains deeply sheltered from the outside world. She becomes the target of a deceitful marriage scheme designed to strip her of her inheritance.

Gentleman is a handsome, charismatic con artist who associates with the Lant Street thieves. He dresses carefully to maintain the illusion of being a ruined aristocrat, using his manners to gain entry into upper-class households. He devises a ruthless plot to wed a secluded heiress and have her institutionalized to steal her fortune.

Mrs. Sucksby is the formidable matriarch of a criminal household in London. She runs an "infant farm," taking in abandoned babies for profit, while actively fostering a ring of young pickpockets. She fiercely protects the orphans under her roof and acts as a surrogate mother to Susan. She enthusiastically supports Gentleman's marriage scheme to secure their collective fortunes.

Mr. Ibbs is a locksmith who secretly operates as a fence for the Lant Street thieves. He handles the "poke" (stolen goods) brought in by the young pickpockets and manages the financial side of the criminal enterprise alongside Mrs. Sucksby.

Mr. Lilly is Maud's wealthy, scholarly, and tyrannical uncle. He maintains strict control over his niece, forcing her to act as his secretary and read aloud from his extensive collection of obscure and controversial literature. He keeps his estate heavily secluded from outside visitors.

Flora is a young pickpocket raised in Mrs. Sucksby's household. She introduces Susan to the theater and the realities of their thieving lifestyle before eventually facing the consequences of her crimes.

Dainty is a simple-minded but loyal young thief who lives among the group overseen by Mrs. Sucksby and Mr. Ibbs. She remains a constant presence in the criminal household.

Mrs. Stiles is the strict, unsmiling housekeeper at the Briar estate. She helps enforce Mr. Lilly's rigid household rules and maintains a tight watch over the servants.

Charles is a young servant at the Briar estate who becomes infatuated with Gentleman's refined demeanor. He desperately hopes to leave his menial position and become an apprentice in London.

Agnes is Maud's original maid at Briar. Her abrupt departure from the estate is orchestrated to create a vacancy so that Susan can infiltrate the household.

Mr. Hawtrey is a gentleman and hidden bookstore owner who occasionally visits Briar to view Mr. Lilly's rare books and listen to readings. He carefully guards his reputation while indulging in his private literary interests.

Dr. Christie is a physician at a psychiatric hospital for women. He holds firm beliefs about the fragility of the female mind, frequently diagnosing his patients' distress as the result of overexposure to literature.

Nurse Bacon is a harsh and abusive caretaker at the psychiatric hospital. She uses physical force and intimidation to maintain control over the women confined to the wards.