As with a lot of mystery stories, I think the author sort of did a double-twist thing to make sure most people wouldn't have guessed the ending. It works to a point, but involved a bit too much tedious exposition to justify and even then didn't really manage it. Also, I don't know that much about serious cross country but it seemed like a strange setting and I didn't get the feeling the author knew much about it, and just included it to give the characters an organic reason to be in the woods at any given time.

That said, I don't want to be an overly picky adult reader of a YA book - it's not written for me, and I'm sure younger readers who love a pulpy whodunit to fill the void will have a decent time with this one.