This homage to the slasher genre begins, like many of those movies, with a guy having sex with a younger woman. She's not happy about the outcome of their interlude so she makes herself a drink and puts on some music while he takes a shower. After he gets out he sees "You're Next" written in blood on a glass wall--and her dead body behind it. He's killed by someone wearing an animal mask.
Next, we go to an older couple, the Davisons, who are celebrating their wedding anniversary at their country home, which happens to be next door to where the other two are murdered. The door is unlocked but they just think that the handyman left it open. Then, there's their son, Crispian, who is bringing his girlfriend, Erin, to meet them. He's not too excited--and we find out why once his brothers and sister show up. They are all a bunch of assholes. Things pick up when they are all sitting down for dinner and someone starts firing cross bolts at them. One person is killed and another injured. The wife freaks out and has to go upstairs to bed--but there's an animal masked killer waiting for her. There's not just one killer---there's several of them. Everyone is passive except for Erin, who manages to wound and then kill one of them with a hammer. And she gets better at killing as the movie progresses, something the killers definitely weren't counting on.
What starts off as a typical slasher movie quickly becomes more clever and untypical as some twists are revealed. It's worth viewing just to see the "victim", Erin (Sharni Vinson) kick ass. If you enjoyed CABIN IN THE WOODS you'll enjoy this flick. Highly recommended.