If you decided to join up with Moire and Axle, Uncus will be your go-between, informing you about the situation in Neverwinter. You'll be facing some thieves-related events, such as a demand to pay them a share of your incomes, or to give back them the goods that were confiscated by your men. Eventually it will come to an assassination - when you enter the keep, some thieves disguised as greycloaks will try to kill you. A few rounds later, Axle will send you an invitation to his mansion. It'll turn out that Moire has formed a separate gang now and he wants you to kill her - your reward for that would be further independence from Axle. Moire's hideout is near Leldon's house (the one you visited on Neeshka's quest). To know the password, approach the warehouse in the north-western corner of Merchant Quarter and follow one of the thieves back to the hideout. Inside you'll meet Moire and have to choose - to kill her or to support her and go back to whack Axle. You can just as well kill them both. It's up to you.
The reward is of course the guarantee that you'll have no further problems with the thieves, plus a lot of magical items from the enemies' bodies and hideouts. The outcome on this quest will determine one of the aspect of the game's ending.