A 12-year-old boy named Sho, suffering from a heart condition, moves to an old house in the suburbs of Tokyo to recuperate. There, he discovers a secret: the Borrowers, tiny people only about 10 centimeters tall. They navigate through cracks and crevices, coexisting with cockroaches and ants. Everyday human objects can last them for years, and their one unbreakable rule is to never let humans discover their existence. Arrietty, a 14-year-old Borrower girl, finally gets her father's permission to experience the adventure of "borrowing," but on her very first mission, she is discovered by Sho! Normally, being seen by humans spells disaster for the Borrowers, but a special bond develops between Arrietty and Sho.