After lunch the entire cavalcade—drones in the air, cars and buses on the ground—doubled back eastward, angling south so that the skyscrapers of downtown Houston swung across the horizon on their left. The sky was brilliant blue, interrupted here and there with huge roiling buttresses of cloud. These were blinding white where the sun shone on them, but otherwise a shade of dark gray that, to Saskia the pilot, suggested they were burdened with more moisture than they could handle. They were crowned with wreaths of lightning. She watched one such formation grope blindly for the earth with a fuzzy gray pseudopod. From miles away it looked soft and slow. It was even decoratively framed in a brilliant rainbow. But yesterday on the drive in from Sugar Land they had been caught in one of these. She knew what was going on in there. All the cars caught in it went blind. Most slowed down, some stopped. Collisions happened that would not be visible until the squall had moved on.