JUSTICE MUST BE SERVED/ A GIFT OF SILENCE
The Collective needs a courier to effectively bribe Knight-Commander Harrith with ten Lyrium Potions, thus solidifying the relationship between the Templars and the Collective.
If you chose to abandon Redcliffe during A Village Under Siege then this quest will be unavailable. However, if you activate this quest before arriving in Redcliffe, then it is still possible to do this quest and abandon Redcliffe if you so choose.
There are two options here:
Give the potions to Knight-Commander Harrith (located by the Windmill (Redclife Village Map, L19) or inform Knight-Commander Tavish, located in the Denerim Market District Map, L4, about the illegal dealings.
Knight-Commander Harrith
Knight-Commander Tavish
Note: As is the case with health poultices in Restocking the Guild, the quest will accept any 10 potions of lyrium, starting with the least potent ones in the player's inventory, then the next least, until the number of 10 is reached. While the wording may suggest otherwise, it does not specifically require Lyrium Potions, so the most economical solution would be to have at least 10 Lesser Lyrium Potions in your inventory before handing in the quest.
Results
If you talked to Harrith you must return to the Mages' Collective for your reward.
If you talked to Tavish you get your reward after your conversation with him.
Rewards
1 Gold
175 XP
Betraying the Collective by choosing Tavish on this quest prevents the Defending the Collective quest from being accessible.
Notes: Due to a bug it is possible to side with Knight-Commander Tavish after completing the quest with Knight-Commander Harrith. In this case he will take 10 more lyrium potions and a "note" from you and reward you with an additional 1 gold and an appropriate amount of XP (although the quest log will remain unaltered). This was not the original intent for the quest you were suppose to choose one or the other.
There is a bug in which you automatically side with Tavish after you speak with him, even if you don't chose the option to actually pick his side