The Guildmaster informs you that Twinblade hired a band of highly skilled assassins to come after you. From this point you will encounter several of them until later in the game.
You can find more information about each encounter in the following walkthrough.
The Assassin Attacks quest is very important if you wish to complete the Hidden Booty Hunt optional quest.
When you visit Knothole Glade you will encounter the first assassin that was sent after you. He comes towards you from the narrow path thats opposite the Demon Door.
The assassins are skilled opponents, so try to block their attacks before retaliating. Each of them drops a different reward, and once you kill the first one you will receive a Doll of You.
However, this is not part of the quest Collect the Hero Dolls. You can find another assassin in the Prison Path area after you rescue the Archaeologist. When you go back to the dock in Prison Path you will encounter the assassin along the way.
The third assassin that you can kill is waiting for you at the windmill in Windmill Hill area. However, he spawns only if you get inside or on top of the windmill. Be careful on your way back or youll bump into him. The assassin that is in the Witchwood Cullis Gate area can be easily missed if you dont know where to look.
From the central point on the map follow the narrow area that leads to the Focus Site and the assassin should come towards you after a few seconds.
You can find the final assassin once you are able to travel to Hook Coast. Simply go by the bell in the north-east side of the town and he will immediately come after you.
After you defeat the last assassin you complete the side quest, but most importantly you receive the Treasure Clue 3 reward.
Assuming you completed all other side quests up to this point you now have all the clues for Hidden Booty Hunt quest.