Arrietty, a tiny teenager, lives with her parents, her brothers and her sisters in the recesses of a suburban home, unbeknown to the homeowner and housekeeper. Like others of her kind, Arrietty remains hidden from her human hosts, but occasionally ventures forth from beneath the floorboards to borrow sugar cubes and other supplies. A secret friendship returns when Zach Loud sees Arrietty again, but their relationship could spell danger for Arrietty's family.