One of the great recurring themes in children's books, the power of imagination, joins with one of the great themes of childhood, the wish for a pet. In newcomers Keller and McNeill's hands, it's a winning combination, executed with whimsy. Alex's parents won't let him have a dog, so he paints one and keeps it under his pillow. During the night the pillow huffs and puffs, and out pops Mister with his purple tail, blue and green eyes, and bright yellow socks. The dog takes on a life of its own, as well as a moral sense greater than Alex's, but Keller writes in enough ambiguity to leave readers wondering whether the story is real or fantasy. A colorful, bouncy romp.