Beneath the floorboards of a sprawling mansion set in a magical, overgrown garden in the suburbs of Tokyo, tiny 14-year-old Arrietty lives with her equally tiny parents. The house is occupied by two old ladies, who are unaware of the existence of their miniature tenants. Arrietty and her family live by "borrowing". Everything they have, they borrow or make from the things they have borrowed. A sugar cube here, a scrap of material there.

But only a little each time, so the ladies do not notice. Arrietty's parents have always warned her: "Never let humans see you." Once seen, little people always have to move on. But the adventurous Arrietty doesn't listen, and soon she gets discovered by Sho, a 12-year-old human boy who lives in the mansion. The two begin to confide in each other and, before long, a friendship begins to blossom...