When I’d first decided to press ahead with my investigation of Mama G’s death, I’d thought that the warm sunshine of Aztlan would be a welcome change from the chilling rain of Seattle. As soon as we reached Tenochtitlán, I realized my mistake. From the air, all that can be seen of the capital is a thick brown smog that obscures the ground. The occasional skyscraper or upper layer of an enormous stepped pyramid juts through this obscuring haze, but otherwise the sprawling mass of dun-colored buildings that fill the highland valley are completely hidden from view. Somewhere below the haze, nearly eighteen million people (closer to twenty-two million, if you count the SINless) eat, sleep, live—and breathe.