Batman and Robin were inside Arkham Asylum. The commissioner had called them when a riot broke out, no doubt administered by the Joker. Criminals were running amok and most of the guards were down. Batman and Robin had dealt with riots before, but this was the biggest one yet. They were fighting criminals left and right, one of them had escaped down the hall, Batman and Robin were on his tail. They came around the corner into a cell, the door locked behind them and the room filled with gas. Robin collapsed first and the Dark Knight fell to his knees as the invisible gas filled his lungs until he couldn't breathe. He had never encountered this gas before, his eyes filled with dots and the room went black.