The Elder Scrolls IV: Oblivion/Ocheeva Quests

Ocheeva is the female Argonian in the Dark Brotherhood and seems to be a bit humbled by your skill.

The Lonely Wanderer
You will need to kill a High Elf named Faelin in the Imperial City, but little is known about him within the Brotherhood. Find and speak with the first High Elf you see in the Imperial City for info on Faelin. Their most likely response is he resides in Tiber Septim Hotel. If your High Elf doesn't know, find another one and ask. Find the Tiber Septim Hotel in the Talos District and talk with the proprietor about Faelin. She most likely won't give you much information unless of course you already have a high disposition with her, if not, raise it. She reveals Faelin is a junkie, doped up on Skooma and infact does live there along with his fair lady. He visits her for a couple of hours in the night before heading back out to get high.

Go upstairs, if Faelin is there and you do want the bonus, DO NOT KILL HIM. Faelin and his girl's room is the first door to the right. Talk to Atrena and max your disposition with her, so she tells you where Faelin gets high. Head over to The Elven Gardens and follow your quest marker to Lorkus's House. Once inside Lorkus's house hunt down Faelin and slay him. Talk to Orcheeva back in the Cheydinhal Sanctuary.

Whodunit?
This is one of the most fun you'll have on a quest. Five people all targets are locked in a house (willingly) and told to search for a treasure chest with gold and the key to the house. The catch? There is no treasure and the key is with the assassin sent to kill them all. You.

Heres where it gets fun, if you can do it without being seen then you get a bonus.

The first target will be the guy who goes upstairs to take a nap, don't stab him or the dark elf woman will walk in on you. Sneak into the corner that can't be seen from the door and shoot him with an arrow. For fun talk to everyone and watch their reactions.

Next target should be the woman who comes upstairs, no one will come upstairs so be as loud as you want.

Third should be the rich elf. He hangs out downstairs and it's easy to get a sneak attack on him that no one sees.

With three people dead the old woman goes paranoid and the nord will head down to the basement to get himself nice and drunk. Follow him down and kill him by any means you see fit.

Lastly is the old woman. Speak with her and she won't even suspect you in your black clothes. Kill her as you see fit there's no one left to see you.

Of Secret and Shadow
This isn't so much a quest as a changing of the guard. Ocheeva tells you that Lucien Lachance wants to talk to you and hands you a note. Read the note and it tells you to meet him in person away from the sanctuary and not to show the note to anyone else.

Now head out of town and go to the base where Lucien wants you to meet. Don't head inside though. Walk around the base and look for a large hollowed out tree. Inside is a trapdoor leading straight to Lucien without going through the Skeletons and Ghosts on the way to him.