The goal is to create a chain of people. They don't know each other. No one knows where it starts or where it ends. All they know is this: they will receive information of their task. They will be given two pieces of paper: one, which they can open and will have the instructions for them, and the other one, sealed, to be passed along to the next person in the line. They don't do stuff online because it will leave traces. That's the basic rule that everyone should follow. The pieces of paper are burned after the mission has been accomplished. 

This is the scheme of that dark side of the world. Everyone is oblivious of the boss or of the goal, so what can they tell to the police if they get caught? The mastermind will never get caught, and the process will still continue even if people get pulled out of the chain. Because inside those letters, there would always be a plan B.

Every person is driven by fear. Even if their task just doesn't make sense to them, they still do it anyway. They've been given the condition that if they fail to do their mission, they will suffer the consequences. And if they show any hint of resistance or hesitation, they will be killed. 

You've been told: a huge sum of money will be in exchange of carrying out the task. A very tempting offer, this one is, especially for people from the slums. Do you accept it or not?  Unknown to you, there's no choice to make really. After executing your mission, you attempt to go back to normal life and release yourself from the chain's burden. But no one really gets out. One day, an unknown man approaches you and slits your throat. Remember the basic rule of this line of business? There should be no traces left behind.