Forge-Bound apprentice Garrick has gone missing and Lohara fears he might be dead. He went searching for exotic materials obtained from the Oldwalls, and may have wandered into Brotherhood territory.
The Brotherhood are believed to have a camp in the Twin Rivers area, and that's likely where Garrick went in search of exotic forging materials.
Garrick is found at the Twin Rivers Oldwalls - Depths, to the south-east. Upon encountering him, you can use Lore 52 to accuse him of violating Kyros' law, Athletics 52 to intimidate him into giving you tools, Subterfuge 57 to steal them... These options cause him to attack, so you can just kill him on the spot. Lohara technically only wants her tools back.→
Note: On the rebel path, if you are friendly with both the Bronze Brotherhood and the Forge-Bound, you may wish to return to town before the last events of the dungeon quest. If you wait until after completing the dungeon to turn in the quest, you will be forced to make a choice that can cause this quest to fail.
Also, if you granted the Crossing to either the Disfavored or Scarlet Chorus, Garrick will give you one piece of evidence against the respective Archon for A Trial of Archons.