Grace begins service at Riverton Manor in 1914 at the age of 14, taking the position at the strict insistence of her mother. As a young housemaid, she is unusually well-educated for a working-class girl and secretly hides Sherlock Holmes books under her bed. Initially tasked with cleaning the neglected old nursery, she observes the aristocratic Hartford children and feels an inexplicable draw to their private world.

Hannah is the highly intelligent, 14-year-old granddaughter of Lord Ashbury. She chafes against the restrictive gender roles of the early 20th century and longs for intellectual stimulation, secretly studying shorthand for the war effort. She leads her siblings in a private fantasy world called "The Game" and views the societal expectations placed upon her with deep cynicism.

Emmeline is the beautiful and charming 10-year-old sister to Hannah and David. She readily embraces her status as an aristocratic ingénue and favors a conventional, romantic view of the world. She harbors a deep fear of abandonment and often struggles with feelings of jealousy when she perceives her older siblings moving on without her.

Robbie is an artistic and melancholic young man who brings a disruptive energy to the insulated world of Riverton. The son of Lord Hunter and a Spanish maid, he has only recently been recognized as his father's legitimate heir. His presence introduces adult complexities into the siblings' childhood games and immediately attracts the attention of both Hartford sisters.

Teddy represents the pragmatic, business-oriented world of new wealth. As the son of a successful American banker, he enters the Hartfords' social circle as a highly eligible bachelor who can offer financial security to the declining estate. He is conventional in his expectations of marriage and society.

Frederick is the widowed younger son of Lord Ashbury and the father of Hannah, Emmeline, and David. He is a struggling entrepreneur with a history of failed business ventures. He frequently clashes with his independent-minded daughter Hannah and lives in the shadow of his decorated older brother.

David is the 16-year-old brother of Hannah and Emmeline and the heir to the Hartford legacy. He enjoys the freedoms and privileges afforded to young aristocratic men and acts as the central anchor for his sisters' childhood adventures in the nursery.

Alfred is a young, handsome footman working at Riverton Manor who dreams of eventually leaving domestic service to start an electrical business. He provides a warm, friendly presence in the strict environment of the servants' hall and pays special attention to Grace.

Ursula is an ambitious filmmaker researching the events of the 1920s for an upcoming movie about Riverton. She contacts Grace at her nursing home, believing the official historical records and hoping to gather firsthand details about the Hartford family's past.

Mr. Hamilton is the strict butler who manages the staff at Riverton Manor. He enforces traditional Edwardian class boundaries and frequently lectures the younger servants on the importance of remaining invisible and knowing their place.

Mrs. Townsend is the cook at Riverton Manor. She runs her kitchen with efficiency and acts as a staunch traditionalist, maintaining order and acting as a parental figure among the lower-ranking staff members.

Nancy is an upper housemaid who shares an attic room with Grace. She acts as Grace's initial guide, teaching her the strict codes of conduct that govern the servants' hall before eventually pursuing war work.

Katie is the overworked kitchen maid at Riverton Manor. She handles the hardest physical labor during grand dinners and occupies the lowest rung of the servants' hierarchy.

Major Jonathan is Lord Ashbury's eldest son and the heroic heir to the estate. He represents the ideal military figure of his class, setting an intimidating standard for his younger brother Frederick.

Jemima is Major Jonathan's wife. She faces immense pressure to produce a male heir for the estate, carrying the genetic tragedy of hemophilia that has already claimed her two young sons.

Lord Ashbury is the aging patriarch of the Hartford family. He presides over Riverton Manor and represents the declining power and wealth of the traditional British aristocracy.

Lady Violet is the conservative matriarch of the Hartford family. She closely monitors the household staff and actively schemes with her friends to secure wealthy marriages for her grandchildren.

Simion is a wealthy American banker whose modern approach to commerce clashes with the traditions of the British aristocracy. He views the Hartfords' financial troubles as a business opportunity to be leveraged.

Deborah is Teddy Luxton's strict sister. She aggressively polices her family's social standing and monitors those who enter their circle, positioning herself as a warden of patriarchal convention.

Lady Clementine is a close friend of Lady Violet. She frequently orchestrates matchmaking opportunities for the young aristocrats in her social sphere, treating marriage as a strategic alliance rather than a romantic endeavor.

Marcus is Grace's grandson and a successful novelist. He isolates himself from his family following the recent death of his wife, prompting Grace to record her life story on cassette tapes for him to hear.

Ruth is Grace's protective daughter. She worries constantly about the physical and emotional toll that the film studio visit and resurfaced memories place on her elderly mother.

Grace's Mother is a former Riverton employee who raises her daughter as a single parent. She insists Grace take a position at the manor and frequently reminds her daughter of the heavy sacrifices she made to raise her.