There is a crash and the lights go out. Living in a fall out shelter all your life this has never happen. You have trained for this.
it could be anything, a breach at the gate where they outside world is invading, a power outage where the power plant is down, maybe it's a drill but you don't think so.
You and your 3 neighbors open the doors and look at each other in the glow of the red emergency power lights. You better go find out what's going on....