Dragon Age 2 - Justice is a companion quest for Anders in Act 3. For this walkthrough, players will help Anders to allegedly release the spirit of Justice from within him, by acquiring ingredients for a special potion, and then helping Anders by distracting the Grand Cleric in the Chantry. This quest is significant for being a setup for the key plot point of Act 3, even though it is not required to complete the game.

1. To start off, speak with Anders in his clinic in Darktown in Act 3, and ask him some questions, until you get a completion notice on the "Check on Anders" quest.
2. Speak with Anders again until you get the Justice quest accepted.
3. The first ingredient is located in the sewers of Darktown.
4. Follow the quest arrow in Darktown to the sewers.
5. Enter the sewers. You will need to collect 5 ingredients here, all marked by a quest sign on the mini-map. There will be some fights in between, but nothing difficult.
6. When you collect all the pieces, head back out to Darktown through the nearby door.
7. Next, go to the Bone Pit outside Kirkwall.
8. Head down to the mines, and enter them.
9. Much like for the Sewers portion of the quest, you will need to collect several pieces of the ingredient, and kill enemies in between.
10. Collect all the quest-marked pieces. No fights to note here besides the Monstrous Spider in the end. It appears tough but doesn't require any special strategy.
11. Head back out into the Bone Pit.
12. Go back to  Anders' Clinic in Darktown and speak with him.
13. Anders will have 1 more task for you, distracting the Grand Cleric for him. Go the Chantry.
14. Note: Don't get confused by the quest being marked as being in Hightown. It is indeed inside the Chantry itself.
15. For this part of the quest, there will be no quest mark for the Cleric. You can find her in the middle of the Chantry building.
16. Speak with her, until Anders comes in again. You will  then get teleported back to the Clinic.
17. After a short cutscene, the quest will be complete.