After escaping from the belly of a whale, Andrew and his cousin Judy face more dangers from their underwater nemesis, Soggy Bob, in the Great Barrier Reef.
Andrew, his cousin Judy, and Thudd the robot accidentally set off in Uncle Al's latest invention, a Volkswagen Beetle converted for deep sea exploration, and try to prevent the evil Soggy Bob from taking a rare ocean creature.
Still trying to save the giant squid from Soggy Bob, ten-year-old Andrew, his cousin Judy, and Thudd the robot nearly meet disaster at the Challenger Deep, the deepest place in the ocean.