The End of Marguerite.

Finally having brought Marguerite's power to an end, the intrepid heroes who have followed this quest chain must defeat the remainders of her undead and the final foe of the Duality quest chain.

Once these groups are defeated, simply go to the altar and consecrate it. A way opens to escape behind it. Now you must go to the Archbishop and confront him with the accusations that Marguerite has layed upon him.

You can see the rest of the quest by clicking here.