Finish the quest A Friend in the Guard and then talk to Aveline about a potential job. Aveline will inform Hawke that she has information about a possible caravan raid and needs Hawke's help to stop the raiders.
Go to the Sundermount Ambush Site with Aveline in the party. Note that if she's not in the party upon entering, the game forces a party re-selection and locks her in.
The first group consists of two Raider type archers, a melee Raider, and an Elite-ranked Raider Assassin. Assassins are quite deadly and will readily abuse their stealth and backstabbing skills to eliminate your party one companion at a time. As Aveline is the most resilient, she may be able to withstand a single backstab without dying, but no more. If the Assassin is the last enemy in the group they are scripted to stop using the backstab, so it may be a good idea to drop area-of-effect attacks to hit multiple enemies at once. Draw the initial group of enemies to you, then kill the melee attacker while hitting the archers with AoEs, or focus the party's wrath on the Assassin and try to take him down with your most powerful abilities. Keep in mind that raiders are vulnerable to electricity damage, if such attacks and weaponry are available.
Heading south from here leads to a more difficult fight with a total of nine raiders, and among them is an Elite-ranked Raider reaver. His two-handed battleaxe hits with enough force to cause interruptions with just his basic attacks, but the archers remain the greater threat due to their ability to hit from range. They can be fought in reverse order by taking the alternate path, which keeps the reaver off you for longer but spawns raiders directly in front of and behind you simultaneously.
Before the main ambush site is another small group with a makeup similar to the very first. Defeat them with similar tactics, and if necessary pull them back to the start of the level now that you have the room to work with.
Once the main ambush site is reached, try to use a ranged attacker, like Varric, to get the ambushers' attention and then pull back to where your party is. This helps you avoid the traps, and positioning them on the tiny hill to the right just before their clearing gives them a great vantage point to attack the enemies. The Critter-ranked enemies can be easily dispatched with AoE attacks, particularly from a two-handed warrior's basic hits and a mage's Firestorm. Then, the group's assassin can be dealt with before the Normal-ranked reinforcements show up. Having Aveline and another melee hold the chokepoint while two ranged strike from the vantage point gives you the tactical advantage to overcome the superior numbers, even without a great deal of abilities.
Once the area has been searched and all loot and enemies is dealt with, go back to the barracks in the Viscount's Keep so Aveline can report back to Captain Jeven. Jeven will berate Aveline for her actions and "showboating," but her suspicions only grow. She suggests checking the duty roster to figure out who was supposed to have that route. Upon checking the roster, Guardsman Brennan thanks Hawke and Aveline for keeping her safe. The ambush they broke up was supposed to be her route, a single patrol which surely would have resulted in her death. Brennan also informs them that "the satchel," delivered to other guard outposts by the holder during light duty hours, was unusually heavy, and that it has now been passed to Guardsman Donnic for his patrol. Aveline takes one more look at the duty roster to determine Donnic's route. Exit the Viscount's Keep and proceed towards Lowtown (Night).
In Lowtown, follow the map marker to the location of Guardsman Donnic and deal with his attackers (the marker and Donnic will only appear with Aveline in the party), initially consisting of four Critter ranks and a Coterie Leader that behaves like an assassin. The Critter ranks can be dispatched with AoE attacks, particularly Cone of Cold, but five more reinforcements will eventually rush in from the main alleyway, allowing the Coterie Leader to continue backstabbing. The tight quarters also allow her to move between companions with reduced travel distance, putting mages and rogues at greater risk. Thus, the party's efforts should focus on her until she is eliminated. Among the reinforcements is a Normal-ranked Coterie Thug who uses stealth and "stealth-less" backstabs, which are far less damaging and only seem to trigger when the target is deliberately facing away from them.
After rescuing Donnic, it is determined that the satchel contains details of the viscount's office, namely city accounts. Jeven set him up as a sacrificial delivery for the satchel to the Coterie's hands. An aggressive response will yield Varric: rivalry (+5), if he is in the party, whereas a witty response will yield Varric: friendship (+5). Loot the area and the Coterie Leader in particular for The Bann's Backhouse Door, a good shield for Aveline (if only because it is a guaranteed drop and available for free). Once done, head back to the Viscount's Keep to finish this quest. Jeven is promptly arrested and Seneschal Bran appoints Aveline to become interim guard captain.
- Aveline is named Captain of the Guard.
- 400 XP (quest completion).
- Once Aveline is named Captain of the Guard, you can talk to her after leaving the Captain's office. Depending on the final dialogue choice during that conversation you will either receive Aveline: friendship (+10) or, if you choose the rude response, Aveline: rivalry (+10).
- If you are seeking the Supplier achievement, be sure to grab the Elfroot at the Sundermount Ambush Site, on the west side of the looping southern trail.
- When rescuing Donnic, a companion will comment on the satchel's contents, stating, "The seal of the viscount. Office details, city accounts," to which Hawke responds, "Valuable to a guild of thieves." The "chain of command" for which companion makes the comment is: Anders > Bethany > Fenris > Isabela > Merrill > Varric.