Assassin: Knight Takes Queen

What is an assassin to do when he is forced to take a contract he does not want to fulfill? If he is the best assassin in the galaxy, he must fulfill the contract, exactly and to the letter. Even if that target is a well-loved leader, revered by billions, it must make no difference. A contract is a contract. How many must live and how many must die, and will "Quantum Magic" play a part in it?