Set in 1930s London, it tells the story of orphans Pauline, Petrova and Posy Fossil, adopted by the eccentric explorer Professor Brown known as "Gum" and raised as sisters by his selfless niece, Sylvia.

When the three girls are small, however, Gum goes missing for more than a decade. Despite stalwart help from old retainer Nana, Sylvia struggles to make ends meet.

Suffering from failing health, she decides to take in lodgers. Sprightly academics Dr Smith and Dr Jakes are soon joined by voluptuous dance teacher Theo Dane and sweet, melancholy Mr Simpson. Their arrival changes the family's lives for ever.

Pauline, Petrova and Posy are enrolled in theatre school, and put to work on the stage. This suits ambitious Pauline, who wants to act, and feisty Posy, who dreams of ballet stardom. But Petrova, steadfast and loving, longs for a career as an aviator, and suffers great frustration and disappointment.