In Tokyo, the boy Sho has a heart condition and is neglected by his parents. He moves to the house of his Aunt Sadako and her housemaid Haru to wait for a heart surgery, but he is depressed with the absence of his mother. Meanwhile the fourteen-year-old Arrietty lives on the underground of Sadako's house with her father Pad and her hysterical mother Homily. They are Borrowers, tiny people that collect simple things they need in the house. Sho sees Arrietty on the garden and during the night, she participates for the first time of a harvest with her father. Arrietty accidentally drops a sugar cube in Sho's bedroom, but on the next morning Sho leaves the cube near a window in the basement. Arrietty's parents decide to move to another place since they have been discovered by an inhabitant of the house. But there is the menace of Haru that wants to capture the tiny people.