“Lockdown! Lockdown! This is not a drill.” When the announcement is made over the speaker, several high school students rush into an empty classroom and lock the door. There is no teacher – just them. Students who previously ignored each other in the hallways are now forced to communicate and band together to survive. Personalities clash and tensions rise as they deal with the unknown. Will they open the door when someone knocks and pleads to come inside? And most importantly, will they come out alive?