Cassie and Alex have a perfect relationship, or so Cassie thinks. Alex has been trying to break up with her, but she just keeps dismissing his attempts as being funny. Alex lives with his sister Sarah. One evening, Sarah hears a noise in the house, sounding like an intruder. She goes into Alex's room to tell him and Cassie. They too hear the noise, and decide to lock the door and hide until the intruder leaves. They call the police, but are unable to get through due to the circuits being busy. As they begin to realize that the intruder is not leaving any time soon, they scramble to find a way out. As their options are slimming, they discover who the intruder is, and realize exactly how dangerous he really is. This sets them into a panicked frenzy, as the intensity of their situation escalates by the minute. Will they make it out alive, or will this be their last time on earth, because of The Intruder.