as she stared through the glass out at the few , isolated flakes drifting down from asgard , she recalled to mind one of her fathers stories that had so frightened her that she hadnt slept for a week after he had told it to her for the first time : just before ragnarok , the end of the world , three winters would ravage the nine worlds in succession , without intervening summersfirst the winter of winds , then the winter of wolves , and then the winter of swords , together called by the norse peasantry , in low , fearful voices , fimbulwinter .