Part 1: Talk to a woman in the city. Close to the crafting area. She is looking for her husband.
Part 2: Talk to a man in Brookhollow in Meadowlands.
Part 3: Look for Brock in Meadowlands, look for his cart along the main road to Northreach in Meadowlands. Check the southern road from the middle ember ring. Make sure to read his journal.
Part 4: Continue searching for Brock. There are traces on Frog island, at the norhtern dock (walk around the barrel just at the dock)