In his illuminating introduction to Sideways in Crime, an anthology of alternate-history mystery stories, Lou Anders sheds some light on why that might be. It has to do with another genre I like: mystery. Anders makes a compelling case for both alternate history and mystery being close genre cousins since both engage the reader by dropping clues that explain the world or plot. He's right. There is an added appeal to these stories for being two-pronged mysteries that reward careful reading.