One night in Ethshar, a "shooting star" streaks across the sky. Suddenly, people all across the land wake up with nightmares of falling, burning, being buried alive. They wake frightened, disoriented, and, in many cases, with a strange sort of magic that allows them to move objects with their mind and to fly. Some of those who appear especially dazed immediately fly north and are never seen again. This new kind of magic is soon labeled "warlockry."
Until this book, the Ethshar stories seem to have been following a chronological order. This one breaks that pattern and slips back a few years from the previous book to the origin of warlock magic. It's a good story about how people can overreact to perceived threats, fear of the unknown, hasty judgement, prejudice, and a little bit about leadership (both good and poor).