Orlukh gro-Othmog believes that it is time to take vengeance against Tholer Andas, Andothren's leading aristocrat, for his part in selling them the derelict Anbarsud iron mine. His plan is straightforward - his thrall has infiltrated the estate, and will spread rumors aimed at separating Tholer Andas from his extensive retinue. You are instructed to infiltrate the manor's sewer system, making your way through the spa to kill the Nord guard with the key to the vault. Then you are to enter the vault where Tholer should (hopefully) be. According to their plan, Varos and Orlukh will join you to strike the final blow.
Travel by night to Andothren. You'll find an entry to the sewers on the cliffs just north of the Andas Estate, at the source of one of Andothren's many waterfalls. Enter, remove the padlock from the crank, crank open the gate, and proceed through the sewers to the Andas Estate: Baths. You'll find Bormundir, the guard, enjoying a moment of peace in the bath. Speak to him, and you will enter combat - once he is defeated, take the Andas Estate Vault Key from his body.
Re-enter the sewers and exit into Andas Estate: Underground. You'll need to take the elevator in the southeast corner down to the estate's Treasure Vault. On entering the vault, Tholer Andas himself will address you - setting his guards upon you. The fight is made easier by the entrance of Varos and Orlukh, who come to assist. Ensure that they both survive, and then speak to Orlukh once the fight is over. He'll grant you his cleaver by way of thanks, and instruct you to take the Daedric artifact, Namira's Shroud, from the vault. Do so - it's required for beginning the next quest, Namira's Shroud back in Anbarsud.