Sharks, shipwreck, and sunken treasure in the latest adventure trilogy from Gordon Korman.Four kids are on a marine expedition for the summer, diving to explore an underwater habitat that's just been altered by a seismic event. What they find, though, is much more than fish - it's sunken treasure. Can they salvage it without anyone else getting to it first? Will the prospect of wealth set them against one another? And what about those sharks . . . .