Fishermen's Guild Member Linneus:
There are some things more interesting than fish! A while back, someone came around looking for a red treasure box. Honestly, the bait I gave you earlier was designed to find it!
Don't look at me like that! It wouldn't have worked if you would've known what the bait was for! So, did you find it? I'll tell you who my client is when you bring me the red treasure box. You must bring it to me unopened. Use the bait of flame to find it.
Remember, your fishing skill must be level 20. Someone may already have found it, so ask around in the market first.