Three teenagers, Aaron, Hannah, and Jay go out at night to investigate reports of a mysterious creature lurking in the nearby river. Jay believes it is real and uses them as bait to try to spot it. Hannah wants to leave, finding Jay's actions reckless. As they argue near the riverbed, Aaron discovers strange eggs or tadpoles. When something large rises behind Aaron, Hannah pulls him to safety while they all flee in the car. The next day, police investigate the same area, concerned about liability if the encounters are reported. They decide to put up pollution signs to discourage people from the river rather than address the actual threat.