THE WORLD'S LARGEST REEF exhibit is coming to the Bayport Aquarium. Frank and Joe are stoked for the unveiling of Predator Reef, a three-hundred-thousand-gallon tank that houses small sharks, rays, and thousands of colorful fish. It's also home to the aquarium's new mascot, Captain Hook, a rare and valuable five-hundred-pound giant sea turtle. But instead of a big reveal, the boys get a big disappointment: Captain Hook has gone missing, along with loads of other exotic fish. Is the aquarium the target of a sinister smuggling ring? And can Frank and Joe do damage control before they're trapped in a deadly underwater maze . . . with no way out?