To Catch a Thief
You will only need to complete this quest if you recruited Isabela back in Act 1. You may want to finish establishing a friendship or romance with her before attempting this quest. When ready, head to your estate and you'll be confronted by Aveline and Isabela. Aveline will urge you to skip this current quest and head to the end of the Act, but Isabela will ask you to help her one last time.
Place Isabela into your party and travel Lowtown at night. You'll fight about five Qunari, including a powerful Sten that should be your main target. After the fight tell Isabela that she can have the relic for herself. This may garner you a tad more friendship with her, though it might not be enough in the end.
Enter the building on the right and Isabela will run off after one of the smugglers. This will leave you in a three battle with the Tevinter and Qunari. The amount of Qunari out number the humans, so you might want to ignore the Tevinter so that they can provide distraction. However if the Tevinter do attack, kill them quickly. As far as the Qunari, take down the Sten Warriors and Saarebas Mages before cleaning up the other cannon fodder.
After the fight loot the building for an extra armor upgrade. Exit the building again and you'll find a letter from Isabela: She's gone and has taken the relic. However, she may have a change of heart. Go into the level up menu and check to see if Hawke posses the Thumbs Up ability from a friendship with the wayward pirate. This can be a good sign that you'll run into Isabela again.
