This can be a really fun mission or a really tedious mission or a really fast mission, depending upon how you'd like to handle it. There is a party at Summitmist Manor in Skingrad (it's just a little way in from the east gate, kind of across the street from your house). You're the (un)invited guest and everyone in the house is your target. How you take them out is entirely up to you. It should preferably be done quietly and privately (which won't be hard to do), but it really doesn't matter.
The guests are at Summitmist Manor to find a chest of gold hidden in the house (there isn't one, so don't bother looking). They are a strange assortment right out of an Agatha Christie novel:
If you want to do it really fast, talk to the doorman (who will give you the key to let you out again), go in, kill each of the guests whenever you can get them alone and leave. Aside from the few golds each guest has (and Neville's armor), there isn't much in the house worth looting.
The reason why it's both fun and tedious is that the way each guest reponds to the situation and other guests depends upon how many people are currently alive and their Disposition toward you, so there are... let's see... five guests times three different Disposition levels (less than 30, 30-70, and more than 70), times five times four times three times two equals ... ummm... a lot of different ways that it can play out (break out a calculator if you're really interested). I am reminded of a "Babylon 5" episode in which an assassin is sent to take out someone with instructions that are someting to the effect of "you are to know pain and then you are to know fear and then you are to die." This is about like that. If you play your cards right, you can get them to kill each other for you. You'll probably have to take out the last guest on your own since it may be kind of obvious who the killer is by that point. But if you played your cards right, the last surviving guest will think that they have killed the killer and are now safe.
You can also play "fun with Poisoned Apples" if you'd like. Get some of those yummy Poisoned Apples from M'raaj-Dar. When you get into the house, collect all of the food that you can find and put the Poisoned Apples out on the table. Then have a seat and wait for people to get hungry. It might take a day or two, but everyone dies and you might even get the last ones to kill each other so you'll have leftovers for later.
Report back to Ocheeva when the last guest is dead. Your reward is your usual fee and, if you weren't discovered as the assassin, the "Night Mother's Blessing" (permanent boosts to Sneak, Blade, Security, Acrobatics and Marksman skills).