Find and kill Darran in the White Tower of Minas Tirith.
A large black cloak.
Find a way into the White Tower, then assassinate Darran and bring proof to the spy hidden in Merethrond.
The reward from this quest is a very special cloak as it does not work like normal containers. It is extremely large, however you cannot simply place things into it and take them out. It can only contain one item at a time and you store the item by doing the following.
To retrieve the item.
The advantage of this cloak is that you can store items which would normally spill (like A phial of Roderick's Dream Potion). You can only store these things whilst the cloak is worn though. If you remove the cloak whilst anything is in the pocket it will fall out (and if it had no lid, spill).
First you need to get the key for Merethrond by completing quest Getting the key for Merethrond. I would suggest getting A key made of brass from Darran, captain of the Citadel Guard as we're going to be killing him anyway. First complete Getting inside the White Tower (I would suggest doing this the killing way, as we're going to need weapons in there) then do the following.
Get the key (if you need to), then continue.
Once he is dead.
get sash from corpse
Now return to Merethrond and do the following.
do unlock west door,2w,sw,4w,n,u,crawl into crate
Now you need to wait, eventually you will see Someone says: So, will you AID me or attempt to DEFEAT me, adventurer?.
You will now leave the box and A nervous little man will be there.
give sash to man
He will give you your reward.
If any of the information here is missing, or wrong, please let us know.