Secret Agent Jack Stalwart: Book 2: The Search for the Sunken Treasure: Australia

Armed with a backpack loaded with ingenious gadgets (and his own common sense), Jack travels thorugh the world, hoping each mission will provide clues to his missing brothers whereabouts. In the meantime, Jack finds himself involved in a treasure hunt.
In one of his most daring exploits, Jack goes down under -- literally -- to investigate the disappearance of a diver off the Great Barrier Reef of Australia. Using everything in his backpack arsenal from anti-puke pills to a morphing suit, an egg-shaped submarine to Disappearing Milk, he exposes a deadly nest of pirates raiding a shipwreck site. Jack has to thwart their schemes, evade their attempts on his life, and escape the primordial hunger of three deadly species: a Komodo dragon, a set of sharks, and the most poisonous predators in the reef, the Irukandji jellyfish. Can he save the treasure and the diver, not to mention himself? Canny and resourceful, Jack will delight readers and impress their parents.