The West End Treehouse Mystery

"As summer approaches, twelve-year-old Matt and Jerry are working on the 'the world's most awesome treehouse' in their western Pennsylvania steel town. All the while, they must keep out of the way of Trio Diablo, a teen gang. But when they venture to the hollow on the other side of the hill in search of more wood, Matt and Jerry stumble into something that may be even more dangerous"--