Jack is a military officer stationed in Turkey while his family is vacationing in Japan. During their stay, his younger son, Kyle, almost drowns in a lake.

Soon after the accident, Jack realizes that something is off. Kyle has changed. He decides to investigate, digs deeply through the realm of Japanese folklore. He realizes that his son may be the victim of a Kappa, an ancient amphibious demon. Now, Jack has just a few days to save his son before the wrathful monster will reclaim his prey, destroying the whole family on its path.