Because the Cast is likely feared and hated by both parties, this makes them a neutral arbiter, right? Quit whining and go talk to the angry, armed men.
Pros:
This is a clearly Good Deed that everyone can feel good about.
Cons:
Peace is a lot more complicated than war.
Fate: 5-10. Be generous.
Example:
“For several months a street gang called the Hacks has been in a fierce war with their rivals, the Slashes, and all of the underwater city of New Hong Kong lives in fear because of this. You will negotiate a peace between these two murderous gangs.”