"Tom and Jamie can't believe their luck when they find a secret entrance to a prehistoric world filled with dinosaurs. Loaded with snorkeling gear, the boys decide to explore the cove itself. But there are some not-so-friendly creatures lurking, including a hungry plesiosaur that wants a snack! Can the boys save their dinosaur friends--and themselves--from the deadliest creature in the prehistoric ocean?"--p.[4] of cover.