New York magazine writer Jennifer Hills (Keaton) is writing her first novel, and decides to spend the summer in a cottage on a lake in the countryside, where she can write it undisturbed.
Three local men, two ne';;;er-do-wells and a gas station manager, are disturbed by Jennifer';;;s independence, and periodically harass her by driving by her cottage in their speedboat, or making sounds at night. One day, while Hills is relaxing in her canoe, two of the men surprise her in their speedboat, grab her boat';;;s towrope and tow her to shore. As she tries to escape, she';;;s met by the other two men in their group and she realizes that they had planned this abduction. It appears they have done so ostensibly so their mildly-retarded friend Matthew can lose his virginity. Jennifer fights but is chased by the men through the forest. They capture her and brutally sodomize and rape her repeatedly in a lengthy and graphic sequence. After she crawls back to her house they attack her again. Matthew finally rapes her after drinking alcohol, but says that he can not climax with the other men watching. While she is being tortured, the other men ridicule her book and rip up the manuscript. As she passes out, the men order Matthew to stab her in the heart, and then leave. Matthew cannot bring himself to do this, and dabs the knife lightly in her blood so it looks as if he killed her.
In the following days, a traumatized Jennifer pieces both herself and her manuscript back together. She goes to church and asks for forgiveness, and then begins carrying out a plan.
First, she lures Matthew back to her cabin and entices him to have sex with her under a tree. As he becomes oblivious to the surroundings around him, she strings a noose around his neck and hangs him. She then cuts the rope and drops the body in the river.
She picks up one of the men at the gas station where he works—he thinks she is attracted to him and wants him. She then stops halfway to her house and turns a gun on him. She orders him to take off all his clothes. He tells her that what happened was all her fault and he feels no guilt—she enticed all of the men by walking around with sexy legs and low-cut tops. She acts as if she believes him, and lowers her gun. She invites him back to her cottage for a hot bath. She manually stimulates him in her bathtub, and tells him she killed Matthew. He doesn';;;t believe her. As he nears orgasm, she picks up a knife she has hidden under the bathmat (which she took from Matthew—he had brought it with him to kill her) and cuts his genitals. He screams and calls out for his mother while bleeding to death. Calmly, she leaves the room and locks him in from the outside. He dies from blood loss and she disposes of him in her basement. She burns his blood-stained clothes in her fireplace.
The two remaining men take their motorized boat to Jennifer';;;s cabin, with an axe in hand. As they attack her, she escapes with the boat and the axe. She then swings the axe into one man';;;s back. The other man swims up, grabs hold of the motor, and begs Jennifer not to kill him, telling her that their treatment of her was the other men';;;s idea. She quotes back to him what he said when she asked for mercy: "Suck it, Bitch!" and turns on the motor, disemboweling him before speeding away. the film ends with a shot of Jennifer smiling as she speeds away