What is the justification for the nobility? Some appeal divine authority. In one world however, being of noble blood really does elevate you above the common rabble. By virtue of magical aptitude.
A caravan is traveling through the desert. The party is hired to capture a man who is in the caravan, and it must be done quietly, so that nobody else knows. They are given the man's name, and the fact that he is a mage, but no other information about him. The catch is that the caravan consists of ten wagons, with at least thirty or forty guards.