Teenagers Reg, Skip, Julie and Pam go out for an afternoon of water skiing on a nice day. They come ashore on an island that is being used as a testing center for a scientist and agents from "an eastern power." They seek to turn the people of the United States into easily controlled zombie like creatures. The agents steal Reg's boat, stranding the teens on the island. The four friends are then held captive in cages able only to speculate on their fate. Though they have already been testing the formula on convicts and drunks, the enemy scientist and agents plan to conduct final tests on the teens before they use it on the rest of America. Meanwhile, two of their friends, whom the captives had planned to meet later, search for their missing friends. After a series of suspicious encounters, they urge the corrupt sheriff to search the island where their friends are trapped.