So the main objective for this quest is to get a journal by becoming one with the shadows and no matter how many times I try to stay hidden, he always sees me and I decide to experiment and went very far away and he still sees me and I know you aren't suppose to defeat him because it would impossible for the amount of mobs that end up spawning...
Right at this part, it should probably show you the objective of the quest and how it's suppose to be done.