Thirteen-year-old Ryan Swanner and his mother just moved to the mountain resort of Black Water Lake. The locals say that beneath the lake's seemingly calm surface, a giant, ancient creature lives. But Ryan's new friend Rita tells him that's just hogwash. She's not afraid to go fishing out on the lake, even though, oddly, the lake seems to be nearly empty of fish.
One day Ryan sees a small animal fall from a tree into the lake — and never surface again. Something is in the lake — and it's alive.