Kithlan is a Redguard noble who resides in the Shivering Isles and is Syl's Steward. In the quest "Ritual of Dementia," he can be convinced to give the key to the Private Gardens and Syl's room to the Hero.
He can be tortured or convinced to tell the Hero of Kvatch that Anya Herrick had been acting strange lately.
Kithlan can be told to imprison Brithaur if the main questline for the Shivering Isles has been completed or the Hero is the Duke/Duchess of Dementia.
To learn more about Syl's routine, the Hero should begin by asking around New Sheoth about Syl to determine the best way to get close enough to kill her.
"What? Do you have business in the House of Dementia?"
- Audience with Lady Syl "You wish to see Lady Syl, do you? The Lady has refused any and all appointments of late. You'd have to try and find her on your own, and I don't recommend that course of action."
- "I can tell you that while she stayts out of the public eye these days, she does still hold audience in her court during the day. You may attempt to approach her then. The Lady has been concerned about her safety lately, so be prepared for a hostile reaction."
After speaking with Herdir:
Conspiracy "No conspiracies here. Go pester someone else."
- Liar, Herdir, torture him! "Please, no!"
- I don't care. Herdir, torture him. "No, please no...."
- "I swear, I know nothing about a conspiracy!"
- Very well. You shall be spared. "Thank you."
If tortured again:
"All right, all right... please, just stop. I don't know anything specific, but Anya has been looking scared lately. More scared than usual. I think something's going on with her. Now please, leave me alone!"
- Conspiracy "I've told you everything I know! I swear!"
- "I am Kithlan, Steward of Lady Syl. Unless you have reason to be here, your presence is unwelcome."