Joey Vass wasn't a swimmer, but since his family bought a house on the shore of a lake, he decided he'd better learn how.  Everything is going along fine until a guy on the school swimming team starts to tease him constantly.

Angered by the teasing, Joey decides to become expert at a different kind of swimming long distance.  Joey swears that before he leaves high school he'll swim the length of the lake:  a distance of twenty-one miles.