when a mysterious mist begins to rise and covers the entire west half of a city, strange things begin to take place, and bad people come into being.
They discovered it at the base of the west wall. A strange that hole seeped darkness: Odorless clouds of shadows and mist, which changed the physical appearance of any living thing touching it. It seemed to do no harm though, and the officials left it alone, fencing the area off and ignoring it.
But, as years passed, the hole grew bigger, and the clouds darker. More people started noticing. The officials tried to keep it quiet, but the mist was beginning to attract attention, and it was frightening people. The trees and plants touching the mist on the street had begun to change, their leaves curling and turning to iron and silver, the bark of the trees turning to black steel. The western side of The City was closed off, as was the western train station. A high wall enclosed the contaminated streets, and a large glass dome covered the top, blocking all chances of the mist infecting a larger area.
The world-on-the-other-side-of-the-wall was dark, lit only by faint silvery light coming from nowhere in particular; the colors were dark, black mostly. Small containers, like fire hydrants in abundance, but shaped like spouts, highly decorated, with a small hole in the side provided a strange resource, a bright light in a dark world, literally, a tiny orb of silver light, neither liquid nor gas nor solid. The officials called it Power, before they decided to never speak of the world-on-the-other-side-of-the-wall, and with it, a person could do whatever they wished, but it was hard to carry, so, unreliable, and it wouldn't work on the east side of the wall.
Explorers discovered this before the world-on-the-other-side-of-the-wall was closed off and outlawed. It was against the law even to mention the fact there was another world so close, to the officials, and the students in school, on the other side of the wall, was nothing. That was the Law: Nothing was on the other side of the wall.
But even so, the Officials couldn't completely close it off, and in the wall was a small hole, a glass window about six inches wide, that gave you a peek into the strange world, the Other Place, the World-On-The-Other-Side-Of-The-Wall.