Pauline is the eldest of the three Fossil sisters, recognizable by her white-blonde curls and blue eyes. Rescued from a shipwreck and adopted by Great Uncle Matthew, she discovers an early passion and talent for acting and recitation. She bears a strong sense of responsibility to help her adoptive family financially, though her early theatrical successes sometimes cause her to struggle with pride and egotism.

Petrova is the middle Fossil sister, characterized by her pale skin, dark hair, and Russian heritage. Unlike her sisters, she lacks a natural inclination for the performing arts and actively dislikes the constant theatrical costume changes. She possesses a mechanical mind, preferring to study airplanes and assist with car maintenance, though she dutifully attends acting classes to help support her family.

Posy is the youngest Fossil sister, easily recognized by her curly red hair. The daughter of a widowed dancer, she arrives at the house with her mother's ballet shoes, which spark her intense dedication to dance. She shows exceptional natural talent and physical coordination but pays little attention to her traditional academic studies.

Sylvia is Great Uncle Matthew's great niece who assumes responsibility for his large home and his three adopted babies. Affectionately called "Garnie" by the girls, she manages the household on a dwindling budget while Gum is away. She constantly worries about the family's financial stability but works hard to ensure the girls receive a proper education.

Nana is Sylvia's former childhood nurse who stays on to help run the household on Cromwell Road. Stern but deeply caring, she assumes the daily caretaking duties for the three Fossil sisters. She possesses a practical mindset, suggesting the family take in boarders when funds run low, and frequently accompanies the girls to their auditions and classes.

Affectionately known as "Gum," Great Uncle Matthew is an eccentric explorer and fossil collector who loses a leg in an accident but continues to travel the world by sea. He unexpectedly adopts three orphaned baby girls from different backgrounds and sends them to live at his London home. He departs on a five-year voyage, leaving behind a bank account to support the household.

Dr. Jakes is a retired professor who rents a room from Sylvia to help the family financially. Recognizing Sylvia's struggles with homeschooling, she generously offers to tutor the Fossil sisters for free. She possesses a vast collection of books and harbors a particular love for William Shakespeare.

Madame Fidolia is a former world-renowned Russian ballet dancer who runs the local performing arts academy. She wears a white practice dress and pink tights, demanding absolute discipline and respect from all her students. Recognizing exceptional talent in young Posy, she takes the girl under her wing for specialized private instruction.

Mr. Simpson is a boarder at the Cromwell Road house who immediately impresses Petrova with his fancy automobile. He operates a local garage and kindly invites Petrova to spend her Sunday afternoons learning about car mechanics. He acts as a supportive friend to the girls, helping them finance their needs through clever but fair business arrangements.

Mrs. Simpson is Mr. Simpson's wife, who returns from Malay to live in London. She acts as a friendly and supportive presence in the house, organizing special treats for the girls and assisting the household with sewing and dressmaking when the sisters secure theatrical roles.

Dr. Smith is a retired professor who moves into the house as a boarder to help Sylvia cover her expenses. Alongside Dr. Jakes, she takes on the responsibility of tutoring the Fossil sisters in traditional academic subjects, ensuring they receive a proper education despite their financial constraints.

Miss Theo Dane is a dance instructor at the Children's Academy of Dancing and Stage Training who rents a room in the Fossil household. She quickly spots Posy's natural inclination for movement and arranges for all three sisters to train at her academy.

Winifred is a talented student at the academy and a frequent rival of Pauline at auditions. She comes from a large family with a sick father, making her desperate to secure acting roles for financial support. Her situation offers Pauline a humbling perspective on the realities of poverty.

Miss Jay is a teacher at the performing arts academy who helps facilitate the older students' transition into professional theater work. She guides the girls through their auditions and delivers the casting decisions for major productions.

Madame Moulin is the French teacher at the academy. When Pauline becomes frustrated by having to wait to turn twelve before she can work professionally, Madame Moulin shares a story about a veteran actress to teach her that performers must always remain willing to learn.

Mr. French is the managing director of a major stage production. He maintains strict discipline in his theater and does not tolerate diva behavior, delivering a necessary scolding to ensure his young actors remember their professionalism.