3. Blindsighted
After rising the ranks of the Thieves guild practically in no time at all, after becoming a Nightingale, a secret division of the Thieves guild hierarchy and after earning the respect of your tea-leaf brothers -in-arms, its finally time to remove the thorn in their side:
Mercer Frey. A slippery devil to the end, Mercer had been your leader in the previous chapters of this quest chain, but upon investigating a traitor in the midst you discover his betrayal. And hed bested you previously too so completing this quest signifies the fruition of your revenge. Mercer uses an invisibility spell along with some fairly powerful offensive magic and after the fight is over, the chamber youre in will start filling with water prompting you to search frantically for an escape. Its a sufficiently epic ending to the quest chain and leaves you as a fully-fledged Nightingale, and the new leader of the Thieves guild. Dont mind if I do!