Mason burdened you with a difficult choice: slay the leader or set him free. It is your duty to decide.
Justice Done is a subquest of Seeking Salvation. Although it's optional, it will complete successfully regardless of the outcome.
The Arisen has the choice between killing or sparing the Salvation leader Marcelo.
After defeating the Undead summoned by Elysion in The Catacombs during Seeking Salvation, surprisingly Mason will appear. He invites the Arisen from behind locked doors to join him for a talk and unlocks the door. Upon entering, a cutscene triggers showing that Mason has captured Salvation leader Marcelo, who's lying on the floor pleading with Mason. Mason suggests it'd only be trouble if they let Marcelo go and leaves him to the Arisen, initiating Justice Done.
Decide the Leader's Fate
The Arisen now has to decide the Leader's fate:
- Kill Marcelo. Inflicting any form of damage on him causes him to die.
- Don't kill Marcelo and leave the area. Just a moment later, the Arisen can hear Marcelo getting killed by Mason.
The quest completes successfully by making either choice, but there are different consequences:
- Killing Marcelo pleases Mason. He says that he can trust the Arisen and sees you working together again in the future.
- Sparing Marcelo causes Mason to kill Marcelo himself. Mason then expresses his disappointment and announces that he will now part ways with the Arisen.
This decision will lower Mason's Affinity. He will cease doing business with the Arisen, which includes the quests Chasing Shadows (which will cancel if it has already been accepted but not yet completed) and A Promised Meeting.