Sarah (Kate Bosworth) invites her childhood friends, Abby (Katie Aselton) and Lou (Lake Bell), to a remote island that they once spent time at in their youth, in hopes of bringing their distant group back together. Though Abby and Lou are reluctant, they go with Sarah to the island. While there, they use a hand drawn map to try to find a time capsule they had buried as kids. They give up after Abby picks a fight with Lou over Lou having slept with her boyfriend years ago, something Abby has never gotten over and which ruined their friendship.
On their first night while camping on the beach, they run into Henry (Will Bouvier), Derek (Jay Paulson) and Alex (Anslem Richardson), three veteran soldiers who are hunting on the island. Lou recognizes Henry as the younger brother of a former classmate and Abby invites the three to camp with them. While drunk, Abby flirts with Henry and eventually takes him into the woods to make out. When she tries to stop, Henry becomes aggressive and tries to rape her. Abby hits him in the head with a large rock.
Hearing Abby’s screams, the rest of the group come running and find Henry dead. Abby tries to explain what happened but the men don’t believe her and become enraged that she’s murdered their best friend. Derek and Alex knock the three women unconscious. When they wake, they are tied together by the wrists on the beach. Derek, the more aggressive of the two men, is adamant about killing them, but Alex tries to stop him. Abby goads Derek into letting her go so they can fight hand-to-hand. When he does, Lou tackles him as Sarah throws sand at Alex’s face to prevent him from attacking. The three women then separately escape and hide, and the two men vow to kill them.
After hiding separately, they meet up at a childhood fort and decide to wait until nightfall before trying to reach their boat. Upon doing so, they discover the two men have cut the rope that tied the boat to the shore, sending it floating out to sea. Abby and Lou both believe they could swim it but Sarah believes it’s too far and that they’d die from hypothermia before reaching it. As they crawl towards the shore, Sarah loudly protests the plan and runs back towards the tree line where she is shot in the head by the men. Lou and Abby try to swim for the boat but cannot make it, instead heading back to another part of shore. Alex falls down a hill while chasing them and breaks his leg. Lou and Abby return to the fort, take their clothes off and huddle together for warmth. Lou and Abby buried their clothes to fake their deaths. They vow to “stop being stalked and start stalking.”
In the morning, completely naked Lou and Abby find the time capsule and retrieve a Swiss army knife from inside. They sharpen sticks into weapons. As they do, they talk about the past and reconcile. They search the island and find the hunters camping on the beach, with an injured Alex sleeping nearby. Abby crawls over to Alex, prepared to slit his throat. However, she accidentally wakes him and he cries out for Derek. Lou runs at Derek, distracting him and Abby wrestles with Alex, eventually shooting him with his own shotgun. Derek chases Lou and Abby finally cornering them in an open field. He fires his gun, but realizes he has run out of bullets. He draws his hunting knife and the two women attack him from opposite directions. They fight, with a wounded Lou eventually slitting Derek’s throat with his knife.
Lou and Abby swim for the boat. The movie ends with the two pulling into the dock, the fisherman looking at them cautiously.