Lord Rytheran tells you, "Ah, you seek my mnemosyne, do you not? My memories of that long-ago day when I read from the book... Your masters desire it so that they may meddle in this affair and save their fragile settlements from the depredation of the Blight. Well enough. I will give you the mnemosyne you seek if you do something for me..."
Lord Rytheran tells you, "In the ancient garden below, my followers have gone mad, forgotten themselves and their allegiance to me. Regrettably, they had something that is dear to me in their possession when they lost their minds. A ring of some... sentimental value. Find that ring, and bring it to me. I will give you the mnemosyne you seek when you bring me the ring. You will have to kill me to get the mnemosyne otherwise, and I can already see you lack the power and the will to do that."