Jason decides--almost on a whim--to found a new religion with the town's water tower as a god. He convinces Shin, Magda, and a bully--Henry--to follow his new religion. They come up with "rules" and guidelines to follow.
Jason believes it's all fun and games, even though Henry wants to do more dangerous stunts on the water tower, and Shin begins to believe he's talking to it. Shin takes the whole idea to the extreme, and Jason isn't sure how to talk him out of it. Jason soon realizes the influence he has over those around him.
A great example of the influences you have on others--without knowing it. The book is a short, fast read, with compelling characters. This book and the Gospel According to Larry have some of the same themes.