So. You're here.
Enter the back door of the Nasher meeting house and kill the Xorlarrin spy.
Now that I have people in place, I have another task for you. Members of House Xorlarrin tend to be as paranoid as they are crafty. When my hired hands launch the surprise attack, doubtless the Xorlarrin spy will attempt to escape. All the commotion will probably attract more Nasher attention as well.
Go back to the Nasher meeting hose and enter through the back entrance. Listen at the meeting room door and wait until the attack starts, then kill the Xorlarrin spy as he tries to escape. You'll probably have to hold off some Nasher reinforcements as well.