Head south from the Aman'lu teleporter, turning southeast just before the South Gate Sign. Head southeast over to the empty house and open the door if this is their first visit. Enter and they'll find a sparkly Intriguing Stone on the table in the northeast corner.

You need access to Kalrathia, which occurs in Act III, Chapter I (Restore Kalrathia's Water), in order to continue this quest. When ready teleport to Kalrathia and head down the southeast stairway, then turn and head southwest down the relatively narrow street until encountering the door to the Magic Shop to the west. Enter, turn to the south, and note the star on your small compass map. Head forward and speak with Enchantress Valeria. Select the number two option to tell her that Danadel from Aman'lu sent your party to see her. She will tell you some more about the Assassins and ask that your party bring her a special Dwarven Mythril Ring from the Mines of Kaderak.

You need access to The Upper Mines of Kaderak, which occurs in Act III, Chapter IV (The Mines of Kaderak), in order to continue this quest. Return to the Kalrathia teleporter and travel to the Southern Desert of Kaderak. Head east up the hills, then north up the next hill and continue north to the Kaderak Mines elevator entrance site. Move around to the east side and enter so our party can throw the switch to bring the elevator up if they've previously teleported out of the mines. Get on and be prepared to battle enemies coming in from the other three sides, then throw the switch again to descend into the Upper Kaderak Mines. Head south down the long passageway and continue south until reaching stairs. Head up two stairways, then turn east and enter the doorway. Head to the rear of the room and activate the switch on the floor to open the secret room beyond. Enter the room and get some gold and the Dwarven Mytrhil Ring from the clearly visible large chest. Teleport back to Kalrathia.

Head down the southeast stairway, then turn and head southwest down the relatively narrow street until encountering the door to the Magic Shop to the west. Enter, turn to the south, and head forward and speak with Enchantress Valeria. She'll enchant the ring and return it to your party. She notes that your character wearing the ring will be able to see the Assasin as long as the ring is worn. Equip the ring on any character, then head east out of the building and enter the travern to the south. Turn and go through the double doorways to the east. Head up the stairway and enter the room, where Innkeeper Angus awaits, and you can see the orange question mark above Merchant Kendril's head in the room beyond to the north. Head through the northern doorway and speak with Merchant Kendril to cause the Assassin to appear.

Engage Luun the Assassin in battle as you would with any other enemy and defeat him to collect Luun's Deathblade longsword Citaa and shortsword Giethaa as spoils of the battle, which completes this quest.

Although your party can Speak to Merchant Kendril again to receive a small reward and very begrudging thanks for saving his life, plus return and give the good news to Danadel in Aman'lu if you wish.