Mouse is small for his age and tired of being teased about it. Then one night he discovers, much to his surprise and delight, that he fits perfectly (well, almost perfectly) into the Undergarden, a subterranean world beneath his backyard. Mouse befriends the Undergardeners—and helps them keep their existence safe from the dangerous world uptop. All that, and he never has to change out of his pajamas!<br><br><br>