Sub-titled an ""Odyssey of Innocence"" -- there's a little more than just a gee-whiz naivete to this story of Julian, a nine-year-old boy who s-s-stammers and whose father thinks he's a s-s-sissy, who takes off from San Diego to Washington, D.C. to patent his soap bubble gun. Aboard the bus, later hijacked, there are a few dangerous characters including a killer -- the kid shows himself capable of quite some heroism -- but the man he least suspects, his mentor-protector Frank Marshall, is the one who betrays him . . . into growing up quicker than he might have otherwise. That's about it -- for that readership which likes to be heartstrung along.