Winter and Night, by S.J. Rozan

Uh-oh--yet another List Author.

This series features P.I. Bill Smith and in this book we meet his family, such as they are since he hasn't actually seen any of them in decades. Yet, his nephew Gary shows up unexpectedly, just long enough to make it clear he's in trouble and then disappears again. Even though everyone involved wants Smith to back off, he feels compelled to nose around, "stirring up trouble."

Somehow, Rozan weaves together high school and small-town sociology, bullying, and family history without losing the flow of suspense.