Karmic Justice is the official name for an unmarked secondary quest available in The Witcher 3: Wild Hunt. You can obtain the quest by walking into the Novigrad suburbs near the river, between the Tretogor Gate and the Southern Gate at night, between 10pm and 1am; or at other various points during the day.
You will find three elves that are about to murder a merchant. If you talk with them they will tell you the merchant sold poisoned fisstech to their young ones, causing them to suffer a painful death, and now they've come for revenge.
You can ask about searching the merchant to check if he has fisstech, but the elves will say they couldn't find anything because he's already sold everything. The merchant will deny the accusations and pledge Geralt for help.
If you decide to help the merchant, due to there being no evidence of him selling fisstech, you will be rewarded with 25XP and 50 crowns should you succeed in keeping him alive.
Additional Info Edit
- If you decide to let the elves carry out the punishment you will not receive any reward.
- If you wait too long before interacting with them, or you just walk away, the elves will initiate combat and you will not be able to stop them from killing him.
- If you aren't careful during the fight, one of the elves will try to kill the merchant while you are fighting the others.