When I walked into the E3 demo room for Metro 2033 sequel Last Light, I was immediately presented with a small, thin military-green bag. Inside it, I found an actual, factual gas mask – sturdy yet pliable, and reeking of fresh-off-the-assembly-line rubber. It might seem like a curious object to take home from a gaming convention, but given the events that unfolded during Last Light’s demo, I can’t think of anything more fitting. So what follows is the story of a videogame. And also a gas mask.