"I sucked at math," T.R. remarked as he piloted the flock on an obstacle course among the skyscrapers of downtown Houston. This was just a few kilometers to the east of the posh leafy neighborhood where they had lifted off a few minutes earlier. It was not, Saskia suspected, the important part of the tour. It was just T.R. getting the touristy bits ticked off the list, making sure the drones were all working.