The narrative tells the story of Ray Waller and his family who face a dark evil lurking beneath the surface of their backyard swimming pool. After Ray receives a neurodegenerative diagnosis, his professional baseball career is put on hold. He relocates with his family to a new home, hoping to recover his strength and return to the field. With a brand new pool in his backyard, Ray takes up swimming as a form of physical therapy. He soon realizes what these dangerous waters hold for him.