You never know what you'll find on the other side of the door. A group of popular high school students learn this lesson the hard way when they stumble into the path of a vicious killer. The gruesome result leaves this town in horror as two battling detectives work to crack the case. Suspicions arise as the school recluse is seen wondering late at night. The game of who-done-it gradually unfolds as the remaining survivors fear the worst: a knock that no lock can withstand.