A 16 year-old girl, Liberty Wells, who goes by Libby, returns to her family lake house after summer camp. While on the drive, her mother, Michelle Wells, a romance novelist, offers to let Libby practice driving. After arriving at the house, Libby meets her mother's new boyfriend, John, an aquatic geneticist, who gives her a bracelet with symbols for the goddess of fertility. During dinner, John explains that his work involves trying to help creatures adapt to changing environments. Later that night, Libby goes to the kitchen and she hears loud sexual moaning, and runs back to her bed. John stands in her doorway and lingers while Libby pretends to be asleep.The next morning, Michelle and Libby dig up time-capsules buried in the yard, and they have an argument about Libby thinking Michelle doesn't care about her grandparents until Michelle tells Libby she felt unwanted by her father. Libby explores the lake and is bitten by a large insect and John helps her. Libby returns to the house to find that Michelle is ill, and Michelle reveals that John asked her to marry him and she said yes. Libby goes to the basement to speak to John, and learns that he is working with parasites. Libby starts to menstruate and when John sees the blood, he attempts to clean it up with his shirt, and touches her. They return to the house and while Libby showers, John sneaks into the bathroom to smell Libby through the curtain. Libby removes the bracelet given to her by John to find a red mark on her wrist.Libby texts her friend Marley and asks her to come to the house. That night, Libby wakes up and sees John walking into the lake which is emitting red lights. John suddenly appears, completely dry, and tells Libby that he suffers from sleep-walking.The next morning, Michelle sends Libby into town to get medicine and a pregnancy test, and while there, Libby follows a man who looks like John down the street with another woman. Libby returns to the house and tells Marley that John touched her inappropriately, and Marley says she's going to tell Michelle. After waking up, Libby finds Michelle and John, and Michelle says that she is pregnant. Libby is disappointed and Michelle thinks that she is making up lies about John touching her. Libby sees that John has a nictitating membrane and tries to pull Michelle away from John but Michelle slaps Libby. Libby reveals Michelle's age which is forty-two not thirty-five then John leaves. A while later, Libby investigates the basement and notices symbols on her wrist where the bracelet used to be. She discovers Michelle in a tank attached to an IV, with the same symbols on her wrists and on the walls. Libby hides while John watches Michelle give birth to a dying creature.Libby calls the police and discovers Marley's body in a water tank being devoured by parasites. John attacks Libby as she tries to escape with Michelle, and she wakes up tied up in a basement. Several men who look identical to John appear and start to peel the walls back to reveal many unconscious women in water tanks. John regurgitates a glowing substance and forces Libby to consume it. Libby awakes in a row of water tanks containing other women apparently in pupae. As water fills her tank, she initially bangs on the glass but then she smiles when she realizes she can breathe underwater.(copied from Wikipedia)