The mission goes underwater this time as the world’s largest reef come to Bayport for an exhibition. Two guys from Bayport have been solving mysteries for the town but they need some fun too. First, it was the ride in The Vanishing Game which crazed them, and later all they got was a case of the missing girl at hand. Thus Joe and Frank are never given a chance by the author Franklin W. Dixon to enjoy fully during the series. With the coming of the biggest reef in their city, the hardy boys get excited because they would get a chance to see a different kind of fish. Also, the reef has a giant turtle in it with the name Captain Hook.
Predator reef comes to the city, to the surprise of Joe and Frank it does not appear to be as colorful as expected by them and also the people of the town. Several of the fish that were promised never approached Bayport and the main celebrity i.e Captain Hook was also missing. Hardy boys just leave the fun once again and come to the business-like tone that they adopted in Into Thin Air. Some smugglers are trying to transport these rare underwater creatures to a different land and Joe along with Frank has to stop them. They got to do it fast or they would die a terrible death under 300,000 gallons of water.
Blurry voice is given to the two by Tim Gregory when they are found underwater in the novel. It is done to portray the haste that is found in the two characters when they are in the water.
