The Master of Disguise

The detailed instructions on searching for the thief will be given by Mihile, the Chief Knight of Light. I better talk to Mihile.

Apparently, the member of the Black Wings has yet to escape Ereve. If we just search the island thoroughly, we may be able to find the culprit. First, I'll need to visit Neinheart and receive a Investigation Permit, followed by a thorough search of Ereve to find Master of Disguise. Once I find him, I'll need to defeat him in a battle and bring back The Lost Treasure in the process. The problem is that the enemy, being the Master of Disguise, is adept at transforming into different persons, so I better talk to each and every one of them to figure out who's real or fake.

Master of Disguise [progress]
The Lost Treasure (The Lost Treasure count) / 1

I was able to defeat Baroq the Master of Disguise, a member of the Black Wings, and managed to recover The Lost Treasure.