You can visit Hubert at his shop in the Hightown marketplace, when he will tell you that he finally had a breakthrough in finding who is behind of these raids. Sabin, a Fereldan miner, was caught leaking information. He also claims that he knows Hawke from Lothering. If you proceed with the quest, Hawke will tell Hubert to bring the traitor to his or her mansion.
Note: You can also tell Hubert that you will be back later. This option is quite important if your group is not ready for a fight because if you accept the quest it will lead to a battle without having the option to modify your party before the fight starts.
The next scene is in the mansion, where Hubert hits Sabin. Hawke has the option to ask him to stop or hit Sabin too. Regardless of what you decide to do, Hubert will leave you alone to interrogate Sabin. Then Hawke has 3 options on what to do.
Promise to help him if he is cooperative
Make him realize that many people died because of his actions
Diplomatic/Helpful: Hawke can promise Sabin that he will take care of his family
Humorous/Charming: Hawke will persuade Sabin to return the ill-gotten money to Hubert if he wants to make it out of there alive
Aggressive/Direct: Hawke will make him talk by using more violence
Note: If you choose the diplomatic on the first AND second choices, Sabin will mark on your map(Bone Mine area, in a crate marked "Sabin's hidden stash" in the camp area) the location of his stash(about 50).
Whichever option you pick, Sabin will agree to confess so Hawke leaves and returns back with Hubert and Lilley, a member of the Coterie. The miner will then reveal that the next raid will happen today, in the Dietrich Crossing. Hearing this, Hubert will propose to leave immediately and Lilley will offer to dispose Sabin's dead body on the way out. Hubert agrees and asks Hawke about his opinion.
You can agree in killing Sabin
You can propose to send him to prison instead
A special dialogue choice depending on Hawke's personality can persuade Hubert to let him go. If a humorous Hawke asked Sabin about his money in the previous dialogue, there is an extra choice in letting Sabin go by returning the money to Hubert.
Note: Hubert will agree with any decision you take.
After you make a choice, the party you had when you firstly talked to Hubert will teleport to an area outside Kirkwall. You will soon find out that you were too late in saving the caravan, so you just attack the bandits along with Lilley. Right after you kill the group that ambushed your supplies, Lilley will recognize one of them as a member of the Coterie that works for Brekker. She will ask you to meet her in Darktown and that she will investigate into the involvement of Brekker. Proceed to Darktown where you will find Lilley's corpse. The Coterie comes up and finds you standing over her dead body and ask you if you're responsible. You can either fight them or talk to them. Following the diplomatic responses will implicate Brekker's involvement and of Lilley's intent to dig into what he was up to. They will leave to find out what is really going on. Simply proceed to the next marker that's not far from your position, enter Brekker's Hideaway.
Note: If you decide to fight them by picking the option "Deserve to die" it will give a Aveline: rivalry (+5) and Varric: rivalry (+5).
You will fight 2 groups of Brekker's men (one of which has a Coterie Alchemist as well) before you reach their leader. There is a standard trap (20 Cunning to disarm - 100 XP) before the first group and a complex trap (30 Cunning to disarm - 150 XP) at the stairs with the second group. When you finally find Brekker, you can threaten him to leave your business alone or attack him directly. Either choice results in combat. There are no traps in Brekker's area, but there is a complex chest (30 Cunning to unlock - 150 XP). Kill Brekker, grab the loot, unlock the chest and return to Hubert with the news of all that has transpired.
1000 XP after you get a confession out of Sabin (awarded when arrive at ambush site)
(optional) about 211 XP and random loot for fighting the Coterie Thugs in Darktown. You gain nothing for the diplomatic option, except avoiding a fight.
You will receive 5 and 1000 XP from Hubert on quest completion.
Although the City Map identifies Brekker's hideout as "Brekker's Hideaway", the save and load screens refer to the location as "Arlan's Hideaway" during this quest.