On the top floor of a lovely old Parisian apartment building in the Avenue des Temps Perdus lives the slightly odd Mademoiselle Oiseau. No one knows exactly how old she is. In fact, since she never leaves her house, nobody really knows her at all. Sometimes, though, one can catch a glimpse of this elegant lady with her unkempt curls and endlessly long pearl necklaces when she’s out on her terrace amid her countless cats and birds.

Isabella is a 9-year-old girl who lives in the apartment under Mademoiselle Oiseau’s. She is so unremarkable that she’s practically invisible. One day, when Isabella comes home from school and gets in the elevator, she accidentally presses the number for the sixth floor rather than the fifth. She doesn’t even realize her mistake until she sticks her key into the lock and Mademoiselle Oiseau opens the door.