At her cousin Judi's invitation, Sam and Karen Casper visit Kuau'i, the outermost Hawai'ian Island, planning to vacation and visit a PlanetCare team doing marine research. When they find Karen's cousin has been brutally murdered, they're caught in a web of events leading to an outlawed casino on the Garden Isle, and a clandestine underwater gaming stadium, where drugged ocean creatures are pitted against each other in battles to the death ... a place where they are targeted as victims, slated to die in a subsea arena of doom.