In each story, a team of folks solves a series of puzzles leading to a prize. In Puzzling World..., the story is based around a puzzle-y will left by a prominent citizen, leading to hidden treasure.
The Potato Chip Puzzles tells the story of a driving-around puzzle hunt game. There's team dynamics, inter-team diplomacy, snack logistics,... It feels like a pretty darned good introduction to puzzlehunts. Your middle-schooler will want to tag along for next year's Shinteki after reading this book.
The books don't just have story. They also have puzzles. Some of these are part of the plot. But some of them also come along because our protagonist makes up puzzles when he looks at things. Which might remind you some someone you know.
Yeah, it's YA fiction, so if you're a grown-up, nobody will be impressed that you read them, but these books are quick and fun. The Winston Breen website is pretty cool, too.