A demon is nothing but sin given will and power
A man who makes a deal with a demon is inviting that sin into him. It does more than consume him - it defines him. It wears him. It rots away at the core of his being. Demons can do it to places, too - whole cities, given the chance. They can alter the supernatural landscape.
Here, then, is the result of sin, hubris and impatience, and here is a chance to banish a demon back to Hell and right a great wrong - or to seize power. Which will the characters choose?
Fallen is Babylon is a story for the World of Darkness inspired by and using systems and material from World of Darkness: Inferno. While having this book would be very helpful in running Fallen is Babylon, it isn't strictly necessary, as the relevant systems are reprinted.