The Lost City of Faar by D.J. MacHale (2005, Unabrid...

Fourteen-year-old Bobby Pendragon is not like other boys his age. His uncle Press is a Traveler, and, as Bobby has learned, that means Uncle Press is responsible, through his journeys, for solving interdimensional conflict wherever he encounters it. His mission is nothing less than to save the universe from ultimate evil. And he's taking Bobby along for the ride.
Fresh from his first adventure on Denduron, Bobby finds himself in the territory of Cloral, a vast world that is entirely covered by water. Cloral is nearing a disaster of huge proportions. Reading the journals Bobby sends home, his friends learn that the desperate citizens of the endangered floating cities are on the brink of war. Can Bobby-suburban basketball star and all-around nice guy-help rid the area of marauders, and locate the legendary lost land of Faar, which may hold the key to Cloral's survival?

 this second adventure in the Pendragon Quartet, readers find 14-year-old Bobby Pendragon traveling through the "flume" to Cloral with his Uncle Press, in pursuit of Saint Dane. This waterworld with a vague Australian/Atlantis air will likely intrigue fans who enjoyed the aquatic world of Jules Verne's 20,000 Leagues Under the Sea and the teamwork escape aspect of Journey to the Center of the Earth. Bobby is still uncertain about what happened to his family after he was recruited as a "Traveler," a heroic role that first pitted him against the shapechanging monster, Saint Dane, in the series' debut, The Merchant of Death. It's a radically different life from that of junior high student in Stony Brook, Conn., where his friends Mark and Courtney eagerly await the journals in which he updates them with the latest events from various colorful "Territories." In the fabled city of Faar, beneath the waves, Bobby meets Spader, who is also a Traveler, and quickly becomes his first mate. Unbeknownst to Spader, his submerged city is partially responsible for the peace felt above the surface in the floating habitats. When Saint Dane decides to annihilate Faar, Bobby and his Traveler buddies must race to outwit the villain. MacHale embellishes his science fiction with just enough silly touches to leaven the mood; for instance, when the magic ring that Bobby gave Mark twitches (which means it's about to "deliver" Bobby's journals), it expands so that Mark must remove it, and the glowing stone transforms into a "black hole," spewing musical notes and light. Next up: The Never War, which will feature First Earth, circa 1937. Ages 10-up.