Four college students – Randy, Deke, Rachel, and LaVerne – swim to a wooden raft on a remote Pennsylvania lake to celebrate the end of summer. Randy notices a mysterious oil slick-like substance floating on the surface that appears to chase the girls as they reach the raft. Deke and LaVerne ridicule Randy’s suspicions until Rachel remarks on the beautiful bands of colors on the slick’s surface and touches it. The oil slick pulls her into the water, coats her, and dissolves her alive. The horrified trio are helplessly forced to watch her die.