Way to unlock: Talk to Cullen's scout in Skyhold.
The quest-giver: Cullen's scout (M12,7)
At the beginning of this quest you will meet a scout in Cullen's office. You will learn that he went to talk with Cassandra.
Go behind the tavern and enter the armory by the door near the stairs up the wall. After a cutscene return to Cullen to his office. Here you must decide whether Cullen - addicted to lyrium - should control himself and stop using it, or you give him free hand. No matter of choice you will complete the quest and the consequence will be seen only in epilogue.
Rewards for completing the quest:
- Experience (lots)
- 400 influence points
- 3 power points