Elysana's First Quest
Wayrest Grand Hall
Let's get one little item straight right from the get-go. You're dealing with Tamriel's most dysfunctional family, here. Morgiah seems to be willing to trade her first to be Queen of Firsthold, Helseth is blackmailing one of his father's counsellors in order to advance his little agenda, Barenziah is completely oblivious to all of this and Eadwyre is unscupulous in the extreme. What makes you think Elysana is going to be any different? Don't turn your back on this babe or you'll get something pointy stuck in it.
If you are at least 6th level and have some positive rep in Wayrest Court, Elysana will send you a letter asking you to come see her. When you click on her, she will ask you to deliver a robe to Lord Castillian (why does everyone have it in for this guy?). On the surface, it's a pretty straightforward quest. Simply deliver the robe. But the robe, as you've no doubt guessed by this point, is booby trapped and you're the booby. As soon as Lord Castillian gets the robe, you'll get to fight some Daedra Seducers. There should be three of them and it can be quite a fight for a 6th level character. But there is a way around it and you don't have to fight them all at once. The key is to "Use" the robe. The first time you use it, you'll get to fight a Seducer. The next time you use it, you'll get to fight another. The last time you use it, you'll get the third and the robe will break (disappearing from your inventory). Get the picture? Use it twice, deliver it and then you'll only have to fight one seducer. Well, one seducer and Castellian's guards.
From a game perspective, this quest is entirely optional. You do not have to do it. But if you blow the Underking's quest, Elysana is going to be your only legitimate route to Lysandus' Tomb.