The Magic Star — Mitzi Pool Bridges

When the Delaney kids find a fellow-classmate hiding in their treehouse, they have no idea that when they agree to help him clear his dad of theft charges that they would all end up chasing diamond smugglers in the middle of the night across miles and miles of the deep and dangerous Mississippi River. Then, when they find that they have stepped into an FBI sting operation, they realize just how much trouble they're really in. Finding themselves hip-deep in another mystery, they must once again rely on their ingenuity and wits. You'll enjoy reading how they accomplish this and find yourself reading this story as well as the others in the series over and over again.