Under the floor boards, as cozy as you please, Arriety Clock and her parents, Homily and Pod, live a quiet little life. Why, they just borrow whatever they may need, like a teacup from the dollhouse that is just the right size for them. Arriety longs to go upstairs, helping her father with the borrowing, but after what happened to her cousin Eggletina (an incident with a cat that no one speaks of) it is forbidden. Until the Boy who lives upstairs, so big and so lonely, sees her father. “And that’s how the whole world changes shape.”

Now, to keep Arriety safe, and to ensure they don’t have to emigrate, Pod will teach his daughter how to borrow. The amount of space above the floor is amazing! It almost overwhelms poor Arriety, who just isn’t used to so much. No sooner has Pod moved off in search of brush fibers than Arriety is spotted by a “human bean.” As if that isn’t bad enough, she and the Boy even have a conversation. Now what are the Clocks to do? Boy, however, means them no harm, even if he does pry up the floorboards (their roof!) in order to find their home. Why, he just wants to help, to give them presents. Yes, this might just be a wonderful friendship. Before they have time to get to know each other, however, Mrs. Driver stumbles across the Clock home, thinking it is a mouse nest. In her horrible agitation and fear, she asks the gardener to smoke out “the mice.” Luckily, the Clocks manage to escape the poisonous gases by jumping out the air vent. They must keep their wits about them as they venture across the orchard in search of where Eggletina’s parents live.

As Homily frets over spending the night in an old boot, Arriety wonders at the vastness of the world in front of her. Here it is—the adventure she has always dreamt of. And wouldn’t you know it, but here’s another something straight out of her dreams—another Borrower! Dreadful Spiller. He may be filthy and a little rough, but he’s a Borrower just like her. Spiller helps keep the Clocks safe, and fed, and helps the summer days pass. All summer, Pod goes in search of the other Borrowers, and every evening he returns, more exhausted, having found nothing, until one day, he collapses. Spiller sets off to find the Clocks a proper home where they can rest and be safe. As they wait for his return, snow begins to fall signaling that winter is truly upon them. Once Spiller returns, he leads the Clocks to their relatives, safe and snug behind a fireplace in a nearby cottage, where Arriety is free to go out in the sun and rain and whole wide world.