The old theme of a child who is ""different,"" but whose handicap leads to special achievement, is given a fanciful turn in the flimsy tale of winged Flap, the only Ariel in Treetoptown who cannot fly, and his dealings with the dwarflike, ground-dwelling Stubblocks who build him boats so he can make his own life on the water. After too many pages of scene-and-situation-setting and nautical specifications, Bumprock (a Stubblock) whets Flap's wanderlust with tales of a far-off underwater road leading to stairs in a hollow mountain. But we never discover where they lead, for after protracted wishing and wondering Flap decides to postpone his own explorations until spring. Instead -- and arbitrarily -- the book ends when Flap becomes a hero by rescuing his people from their island by means of his boat, pulleys, and mainland Stubblocks stoutly hauling on a rope. There are other characters with names like Alofta and Updraft (Ariels) and Stumproot (a Stubblock), which indicates the level of the whimsy. It seems that cousin Swampgas was right at the start: Flap will never get off the ground.