Nursery teacher Jenny (Reilly) and her boyfriend Steve (Fassbender) go on a camping holiday to the idyllic Eden Lake, soon due to be overtaken by a gated community, where Steve plans on proposing to Jenny.
After they arrive and attempt to relax, a local gang of chavs (lower-class British youths), led by a particularly unhinged boy named Brett, begin to infringe upon their time together and continuously ignore Steve's requests for peace.
After one chance encounter, the gang's mischievous rowdiness turns to horrific rage, unleashing a whole new side of their danger that throws the couple's vacation into an immediate downward spiral.
What was once the setting for a beautiful getaway turns into the grounds of a fight for survival as the couple are dragged into an increasingly brutal cat-and-mouse game, and must do whatever it takes to get out of the woods.
This film provides examples of:
- Abusive Parents: They're seen on three occasions: first, Jenny and Steve witness a mother slap her child very strongly for running within the pagoda of the restaurant; later, Steve witnesses Brett's father call his son maliciously and threateningly while he's within his house; thirdly, Jenny witnesses Brett's father smack Brett across the face after the latter refuses to obey him.
- Agony of the Feet: While running, Jenny impales her left foot on a metal spike sitting upright on the ground. With the spike protruding through the top of it, she removes it from her foot by pushing it all the way through.
- The Bad Guy Wins: Implied: with Jenny soon to be dead and his father having promised to ensure the town tells the police false information, Brett deletes the videos of the crimes of his gang.
- Camera Fiend: Brett uses Paige to film the gang's acts of torture and murder.
- Corrupt Hick: The gang members, owing to the town from which they come and their parents.
- Cruel Twist Ending: An oncoming vehicle hits Jenny's stolen van on the side as she drives it to escape Eden Lake, and she crashes into the yard of a house during a party. The party members assist her within the house and reassure her. Then, as they learn via phone call of the children Jenny killed, Jenny learns that the owners of the house are Brett's parents and that Paige and Cooper's parents are among the guests. Brett's father takes her into his shower with two other men, all but confirming her death.
- Daylight Horror: In the morning that Jenny wakes after being knocked unconscious, she finds herself tied to her dead boyfriend as the gang pours petrol on both of them and minutes before they ignite him. After that, she witnesses Brett ignite Adam on her account.
- Death of a Child: Adam, Paige, Harry, and Cooper.
- Don't Go in the Woods: Played straight and lampshaded. While driving with Jenny through the woods to Eden Lake, the GPS vocally advises Steve that he's going the wrong way and ought to turn around. It's never explained why.
- Downer Ending: Not an ounce of justice is brought at the end of the day, and every chip seemingly falls into place such that Jenny and Steve's perpetrators get away scot-free. Jenny falls into the hands of the gang's parents in the final segment. Brett's father promises to silence the town when the police arrive, and he murders Jenny in the shower. Brett deletes the mobile phone videos containing footage of the gang torturing and murdering.
- Evil Laugh: As Steve's corpse burns, Brett jumps up and down, laughing.
- Final Girl: It's Jenny against Brett and his gang, but she loses to his father.
- Hope Spot:
- Leaving a mortally wounded Steve in hiding, Jenny searches for power lines of which Steve reminded her and by which she believes she can find her way into town. She finds them and follows them until she impales her foot on an up-turned spike, which wounds her and immobilizes her long enough for one of the town teens to find her.
- Zig-zagged in the final segment. After stealing a van, Jenny drives to leave Eden Lake until the car's struck on the side by an oncoming vehicle, and she crashes into the yard of a house, with locals having a party. They assist her after she asks and agree to help her before she realizes that it's the home of Brett's parents and that several of the others' mothers and fathers, including Cooper's, are in attendance, and they realize that she murdered two teens. Brett's father kills her in the shower.
- It's Personal: Things go downhill real quick for Steve and Jenny after Steve kills Brett's dog.
- Jerk with a Heart of Gold: Steve, who is a bit too aggressive with the gang.
- Karma Houdini: The entire gang except Paige, Harry, and Cooper.
- My God, What Have I Done?: Heartbreakingly, Jenny after accidentally killing Cooper, one of the more reluctant members of Brett's gang.
- Nothing Is Scarier: We don't see what happens to Jenny. We only hear the screaming...
- Papa Wolf: Brett's father, who murders Jenny once he learns she murdered two members of Brett's gang.
- Peer Pressure Makes You Evil: If not for Brett, the gang wouldn't have gone to such horrifying extremes.
- Pet the Dog: Literally, with Brett's affection for his dog. It's after Steve kills her that Brett's intent turns murderous.
- Ring of Fire: Downplayed: after Jenny breaks free of her binding to the burning stake, she grabs a container of petrol, pours some between her and the gang, and lights it, making a chase difficult.
- Screw This, I'm Outta Here!: Shortly after finding Cooper's body and witnessing Brett beat Harry to a dead pulp, Paige decides she's had enough and flees. Unfortunately, she runs into the path of the van Jenny's driving, and Jenny's feeling self-righteous.
- The Sociopath: Brett.
- Teens Are Monsters: Dear God, yes. The chavs execute malicious, escalating torture and murder on Steve and Jenny,and, in the moral and emotional turmoil that they create, Brett kills Adam and Harry.
- Would Hurt a Child:
- Brutally Deconstructed with Jenny. As a schoolteacher, she'd normally never lay a finger on any child, but as a result of the situation she's found herself in, and specifically after being betrayed by Adam to the gang, she's forced to take them on for self-defense. And doing so has negative effects each and every time. She ends up killing two gang members by the end of the movie, both of which were the only ones to actually realize the harm they were causing. But the worst part is when the parents of those kids find out what she's done to them...
- Played straight with Brett, who kills both Adam and Harry.