The unfinished coffee glass slipped from his free hand and hit the paving stones as Milton yanked me along. People all around looked around in fear, asking the same questions as I did. What happened? What is the alarm, and why did the ethereal crystal turn red?

I tried to control myself and not panic. If you turn your back on the tower, it may seem that nothing happened at all. But after a couple of seconds, the city was again filled with the menacing sound of a siren, and the light from the crystal flickered again and became even brighter, wrapping the embankment in an oppressive red hue. In...