Missing - Act 1 Broken World Side Quest
Location: The Blasted Valley
Closest Portal: The Blasted Valley (North)
Objective: Defeat Eliza
Reward: No Reward
Missing is one of the first Side Quests available to you in the Broken World Expansion Pack for Dungeon Siege 2. To begin this quest speak with Soram who is nearby the tents where you first entered the game after starting the expansion. Despite being able to pick this quest up immediately after entering the expansion you will not be able to complete it until you've finished The Mage's Tutor Story Quest.
In order to access the portion of The Blasted Valley that Eliza is in you'll need to be able to open the 'blue flame' doors as well as the vine doors that block your way. To open the blue flame doors you'll need Kanred's Staff from the Kanred the Mage Story Quest. To open the vine doors you'll need to learn the secret phrase which is taught to you after you complete The Mage's Tutor Story Quest.
You can find both of these doors by taking the western branch off of the main path between the two Blasted Valley Teleporters. Check my map screenshot below if you'd like to see exactly where the path branches and leads to Eliza. Much like the Anya quest, Eliza has already become 'Bound' and there will be no talking involved - attack and defeat her then return to Soram in the Dryad Outpost and speak with him.
Soram will attack you when you bring him the bad news but the fight with him is very easy and he'll give up when he gets low enough HP. Speak with him again to complete the quest.