The story takes place in a small town in Florida, USA. A fierce hurricane hit the town when the residents were caught off guard. Hailey (Kaya Scodelario) is a swimmer. During training, she received a call from her sister, who told her that their father Dave (Barry Pepper) was missing. The government ordered all the residents in the town to evacuate from their homes, but Hailey could not abandon her father and returned to her father's home without authorization. Sure enough, in the basement, Hailey found her seriously injured father. If she hadn't appeared, Dave would have died. Now, the father and daughter need to face the basement that is gradually filled with floods, but soon, Hailey realizes that their opponents are not so simple, and there are some evil and violent shadows hidden under the water.