An apocalypse occurred when the world began to freeze over. Most of the world died. The few who survived have formed unconnected cities around gigantic 20 story massive heating towers [one per city] called Generators, the technology to build them is lost. It never gets warmer but the mystery of why it got so cold is unsolved. The Commandress, a powerful woman who rules the city with emblems, her uniform, and her authority, resides in the Generator with the few engineers who can repair it.