Dirk was feeling lost and lonely. His wife Patricia had announced that she was struggling to feel any purpose in her life and had decided to move into an apartment for a time period to sort things out. Dirk is strongly motivated to change something to put his family back together, and decides to sell his share of the business and invest in a summer resort based around a beautiful, remote, spring-fed lake in Arkansas. Unfortunately, he didn't ask enough questions about the history of the lake ... It wasn't until after he brings his three children to stay for the summer that he becomes fully aware of a history of missing persons. Patricia decides to stay at her apartment and continue sorting out her feelings. Within a few days, Dirk's fourteen-year-old daughter is attacked by something that came from the lake. She narrowly escapes with her life, due to the quick action of old Bill Ocherman, who fears that his son has already disappeared in the lake and had begun a nightly vigil. As Dirk struggled to make sense of what has happened, he decides to hire Rodney, a biology student that is also a highly experienced diver. Over time, Rodney learns more and more about the monster that is large enough to block the flow of the underground spring as it passes back and forth between the lake and some underground chamber. But Rodney, friend and expert diver Eddie, and Dirk's son Brad are unable to imagine the size, speed, and mind-boggling power of the strange, underwater behemoth.