After finishing the Act II secondary quest A Servant's Haunt, then speaking to Eldoriath Wilwarin's dead Uncle Threnith Wilwarin's ghost, who's standing next to his nephew in his nephew's home in south Aman'lu, and agreeing to find Lady Levreth in Eirulan and bring her to justice, you'll acquire this quest.

Teleport to Eirulan and head north to the Inn tramway. Take it across to the other side and head around to the Inn entrance. Enter to find that Lady Levreth is standing just inside with an orange question mark above her head. Speak to her and she will break down and admit her complicity in her husband's murder and name her brother as his murderer. You also learn that her brother is none other than the Aman'lu Guardian Commander Wethril. A Dryad guard then enters, apparently having overheard the conversation, and takes Lady Levreth off to see Warden Celia.

Exit the Inn and return to the Eirulan teleporter, then go back to Aman'lu. Head north toward Alt'orn Hall, then head up the stairs and enter. You'll find Guardian Commander Wethril standing to the right of Celeb'hel the Elder at the back of the hall. Approach and speak to him to receive a rather diffident response, noting that Celeb'hel is rather busy. Your character will note that they actually want to talk to him. He pretends to be unaware that his sister is in Eirulan, but when your character confronts him, he reveals that he is guilty of the murder as well as betraying Aman'lu to Valdis by informing him of Aman'lu's Aegis.

After doing so, Speak with Celeb'hel, who'll express amazement at the betrayal, noting he'd been "the very image of truth and justice in Aman'lu for years". Threnith Wilwarin's ghost also appears and thanks your character for setting the record straight and is now finally released from his torment. Your party receives a substantial reward from Celeb'hel the Elder as well as a skill point for each character in the active party (excepting any pets) and this completes the quest.