"Once upon a time there was a little mouse house. It was like a doll's house, but not for dolls, for mice." Not proper mice, but a flannel He-Mouse and She-Mouse with beady eyes and bristle whiskers who stand quite still, propped on their hind legs in the sitting room. Mary knows real mice run and scamper, and disappointed with her new gift, she puts the mouse house away in her room. Meanwhile, down in the basement, a real mouse named Bonnie has been jostled out of her woefully inadequate flowerpot home by her older brothers and sisters. Overlooked by her harried parents and desperate for shelter, Bonnie ventures upstairs and finds the mouse house. And before too long what was a miniature make-believe house becomes a marvelously messy home for proper mice who know how to play, much to everyone's delight.