ok so the movie starts with a group of people in some kind of a square steel room (i guess they are convicts) and they have to choose from four doors each on a side of the room and when they go to a room it can be either a safe room or a trapped room where one or more get killed by various hazards. they find their exit by studying and analyzing serial numbers on the entrance of each room and then predicting what the next room will be and predicting where the exit will be