Bad Medicine
Oblivion: Dark Brotherhood Quest
Ocheeva will send you to Fort Sutch on the West side of the map to kill the diseased Roderick. Roderick is very dependant on medicine to keep him alive. Your task is to switch his medicine with poison. You can, of course, kill him in any way you see fit — but only by poisoning him and remaining undetected can you earn the bonus.
You can enter Fort Sutch either through the main door on the fortress itself, or through a hatch a few meters away. For the main entrance, you'll need to sneak inside and open a gate on your immediate left when you enter the tunnel. The gate is locked, and must be opened with a lockpick. (Spells seem to go right through it.)
Sneak around the tunnels inside until you reach Roderick's bed area. You'll find a cupboard in the area where you can make the switch. Then, retrace your steps out without being seen.
Like other sneaky quests, invisible spells and sneak-fortifying armor (such as your shrouded Dark Brotherhood robes) are very useful.
Return to Ocheeva. You'll receive your gold, and the Deceiver's Finery (a robe that raises Personality and Speechcraft skill).
Speak to Ocheeva again for the next quest: Whodunit?