This mystery can be found in the southwest of Glowecestrescire, in the Forest of Denu near the border to Hamtunscire. When you arrive in the area, you’ll hear a strange woman singing by the small lake.
How to Complete Lady of the Lake
You won’t be able to do anything when you approach the woman at first. Instead, you’ll need to inspect her small house. You can enter it by shooting the lock to the door from the window on the west of the house. Once the lock is destroyed, enter the house from the front door to uncover the horror within. After looking around and looting whatever you can, you’ll find that the lady has locked the door behind you. You now need to escape by moving the object near the window to the west.
When you jump out of the window, you’ll find the lady waiting outside. This time when you approach her, she’ll become hostile and is revealed as the murderer. You now need to kill her to complete the mystery. She isn’t very tough, so this should be an easy task, but she is quick. Once she’s dead, feel free to take a swim in the lake and dive beneath to loot a number of corpses.