Jack, a military officer stationed in Istanbul, is separated from his family, who are vacationing in Japan. During their trip, his younger son, Kyle, nearly drowns in a lake. After the incident, Jack notices something unsettling—Kyle has changed. Determined to find out why, Jack delves into the depths of Japanese folklore, discovering that his son may be the victim of a Kappa, an ancient, malevolent water demon. With only a few days left, Jack must save his son before the vengeful creature claims him for good, threatening to destroy the entire family in its wake.