A classic childhood monster comes out of the bedroom closet (where it frequently lurks in children's books) and climbs onto Charles Tarzan McBiddle's bike. Charles has just removed his training wheels; all his anxieties (``Maybe you're still too little...Your mother thinks so,'' etc.) materialize as a toothy, snouted dragon of a monster that heckles Charles with his own doubts until he gets a grip on his emotional and literal balance and retorts, ``You're a liar,'' then speeds away. The dynamic angularity of Glass's figures perfectly expresses the progress of Charles's state of mind as the monster first balloons in size, toppling him from the little bike, and then dwindles away as Charles's confidence returns and triumphs. In words and pictures, Glass effectively parlays an archetypal rite of passage into an even more universal message. (Picture book. 4-8)