Calimport has been under siege for weeks. The king has sent out the call to heros across the land to come to his aid. You are one of those heroes. You will join up with others of your ilk, sneak around the attacking army, assassinate the general and hope that the army doesn’t turn on you, as opposed to just leaving.
But then, you’re a hero. It’s all part of the job.
This is a 4E DnD campaign set in the Forgotten Realms universe.
After that, take a look at your wiki. There is some more helpful info there.