For more than a century, generations of the O'Malley family have lived on a farm near the Suir River in Ireland. The current family includes Mr. and Mrs. O'Malley, their two children, Brendan and Bridget, and their two pets-a dog and a cat. One day Bridget discovers a basket on their cottage doorstep. It holds a round ball of fur that appears to be alive, but neither moves nor has any extremities. Attached to the basket is a note that reads, simply, Please take care of our rarie. The family takes in the basket and cares for the creature.

The rarie never moves but gradually and imperceptibly grows. Bowls of milk and food the family places beside it disappear during the night. As it grows larger and larger, the O'Malley parents, friends, and relatives become alarmed, and there are calls to destroy the creature. But the parents are reluctant to act because the children are so attached to their mysterious pet. Finally the rarie becomes so large that the parents resolve to get rid of it. One night, after the children are asleep, they push it out of the house and roll it to the river’s edge. What happens next is a delightful surprise ending.