Kounijima is a beautiful island in the Pacific Ocean.there is a tradition there handed down from ancient times that speaks about an ancient site under the sea called "SeaFloorPalace“andtwo real women,Anne Bonney"and "mary Read"who left a treasure there 300years ago.Cano and the other go to Koumijima Island on a vacation and meet with treasure hunters who have gathered there to search for treasure.One of hunters searches for the "sea floor Palace",and gets attacked by sharks and dies.when that happen,Conan and the gang start to investigate...