Dragon Age II Walkthrough: Act 1 : Part 7
Act of Mercy
You get this quest after completing Wayward Son and reading a letter on the Writing Desk at Gamlen's house. Exit the city to the Free Marches, and head to the location marked Wounded Coast Approach. Fight your way through the Dragonlings, making your way to the Southeast of the approach. Meet Thrask in the entrance to the cave. Talk to him, then enter the Runaways' Cavern. Make way into the cave, defeating apostates and skeletons along the way. Find Alain, an Apostate who will tell you about Decimus, and convince Adain to turn himself in. Proceed in the cave, locate Decimus, and slay him. Decide whether to help Grace. The best choice is to agree to help her by lying to Thrask saying they are dead. Leave the caverns. If Varric is in your party, let him talk to Ser Karras, or claim to have killed the mages, for a peaceful resolution. For greater XP and reward, you can tell him you are a friend of the mages to initiate combat. Defeat him, and this will conclude the quest.
The First Sacrifice
Read the Help Wanted poster in the Hightown Market, then go talk to Ghyslain de Carrac who will ask you for help finding his wife. Then head to the Blooming Rose and talk to Jethann. Then go to Darktown to look for Emeric. He is on the southern part of Darktown. Enter the Meeting place. Kill the thugs near him and talk to him. Then go investigate the Lowtown Foundry after dark. After fighting the shades and demons there, go upstairs and find a sack of bones containing Ninette's Ring and human remains. Take it to Emeric in the Gallows during the day. Now go back to Ghyslan in Hightown to complete the quest.
Enemies Among Us
After completing Tranquility, find Macha in Hightown during the day and agree to help her find her brother Kerran who has gone missing after joining the Templars. Go to the Gallows and speak with the Templar Recruits. Then go to Wilmod's camp in the Free Marches map outside the city. Head Southeast, and prepare for a big battle. Then go to the Blooming Rose. You will want to have at least one mage in your group (could be Hawke). Talk to Viveda and then to Idunna. Choose "You can't control me" when she tries have you use your blade against yourself. Then interrogate her and turn her in to the Templars. Go to Darktown to confront the blood mages in their sanctuary in the center of Darktown. Fight your way through the Shades and Abdominations. Locate Tahone and kill her. Then talk to Kerran. Before leaving, pick up the Grimoire of the Apprentice from a sack near the exit. Go find Cullen in the Gallows to finish the quest.
Grimoire of the Apprentice
Take the book you found in the Bloodmages' sanctuary to Boswald at Lowtown Bazaar.