Jackie takes her wife Jules to a remote cabin to celebrate their first anniversary. Jules becomes suspicious when Jackie's childhood friend, Sarah, visits and addresses Jackie as "Megan". Jackie explains that she changed her name by choice but Jules isn't satisfied and visits Sarah and her husband Daniel. Sarah explains that Jenny, a girl who was friends with her and Jackie, accidentally drowned in the lake when they were young and expresses surprise that Jackie never mentioned this. Jackie later claims that she failed to mention Jenny because she believed the accident was her fault, although the police cleared her of any wrongdoing. Jules embraces her wife, consoling her. Moments later, while admiring the view of the wilderness, Jackie shoves Jules off the edge of a cliff.Jackie returns to the cabin, practicing the tearful phone call she's going to make to the police, reporting Jules' death. But Jules, while seriously hurt, is still alive. When Jackie discovers her wife has left, she searches the forest for her, sobbing and begging Jules for forgiveness. Jules is tempted to show herself until Jackie, unaware she's being watched, reveals her concern is an act. Jules flees, makes it to the house, and tends to her injuries. She then makes it halfway across the lake on a boat before Jackie catches up to her. Daniel sees the pair and, despite Jackie's threats, Jules arranges for them to come for dinner that evening.Jackie reveals that she never loved Jules and intends to kill her to cash in on her life insurance policy. It's also implied that Jackie was responsible for Jenny's death. Sarah is suspicious of Jackie. Having threatened to kill both Sarah and Daniel, Jackie forces Jules to pretend everything is normal but catches Jules trying to get help from Sarah. She slits Daniel's throat outside, chases Sarah upstairs and fatally stabs her numerous times. Jackie then forces Jules to help her dispose of the bodies. Jules peeks behind the stuffed head of a bear that Jackie supposedly killed as a child, and discovers a box containing necklaces that Jackie had given to her previous wives, all of whom she killed.Jackie drives Jules back to the cliffs edge where she intends to push her wife off again, but Jules manages to escape by stabbing her with a tranquilizer dart. Jules flees in the car, but returns to confront Jackie. The two fight and Jackie eventually gets the upper hand, knocking her out, and finally throwing her over the same cliff as earlier. Confident that Jules is now dead, she calls the police. Jackie (who is diabetic), injects herself with insulin but starts to feel woozy. She discovers through a video Jules had made prior to their confrontation that the insulin is spiked with hydrogen peroxide. The peroxide causes blood clots in Jackie's system, and after wandering in the woods, she collapses and dies of a stroke.Back at the bottom of the cliff, Jules lies, eyes wide open, presumably dead. As the film rolls over a sea of trees, a sharp intake of breath is heard, miraculously suggesting Jules again survived falling off a high cliff onto boulders.