"I have met Molag Bal, the Lord of Domination. He has asked me to cleanse his altar in the abandoned house in Markarth by luring a priest of Boethiah to him."
This quest can be obtained shortly after entering the city of Markarth. Tyranus, a Vigilant of Stendarr, will ask the Dragonborn to help him search an abandoned house for evidence of daedric activity. Upon entering the basement, Tyranus will proclaim that "This is no ordinary Daedra!" and run for the door, only to find it locked. Molag Bal will speak and command the Dragonborn to kill Tyranus. After he gives the command to kill Tyranus the room starts to shake and the lights turn off then objects start flying everywhere. If the Dragonborn chooses not to kill Tyranus immediately, Molag Bal will convince him to attack. A scroll of calm will not prevent Tyranus from attacking, but casting Harmony will temporarily cease his attacks until it runs out, at which point he will resume his attack. Voice of the Emperor used by Imperials will calm Tyranus. Either way, Tyranus must be killed in order to progress any further. Afterward, journey down to the altar of Molag Bal in the basement.
Molag Bal entraps the Dragonborn in a spiked cage while activating the mace and tells you that he wants revenge on his rival Boethiah (another daedric prince) and her followers. He wants the Dragonborn to lure Logrolf the Willful, a priest of Boethiah who has been desecrating Molag Bal's altar in Boethiah's name, to him so he may break his spirit.
The location of Logrolf the Willful is randomized; any Forsworn camp may host him. Travel to his location and free him. If the QuestNo One Escapes Cidhna Mine has been completed, then the Forsworn holding him may not be hostile. If all enemies at his location are dealt prior to releasing him, he will immediately return to the abandoned house in Markarth.
Once back inside the abandoned house, follow Logrolf back to the altar. He will become trapped in the same cage as the Dragonborn was in and Molag Bal will grant the Dragonborn his Rusted Mace and instruct them to break Logrolf's will. Attack Logrolf (any means of attacking can be used; the Mace doesn't have to be used) until he submits to Molag Bal. Once he submits, the Dragonborn is instructed to kill him. Do so to receive the Mace of Molag Bal and finish the quest.
This is a good opportunity to level up Restoration and the attack skill of your choice (One-handed, Two-handed, Destruction, or even Archery) without fear of reprisal. Alternate between hitting Logrolf until his health is close to 0, and healing him back to full health. You can keep doing this for as long as you want, but be sure you do not kill him and that he does not submit before you are done levelling up.
You can also level up your Sneak skill at the same time by sneaking while performing this method
The whole intro, with Molag Bal speaking, can be skipped if the Vigilant is killed straight upon entering the house.
If you can't find Tyranus, he is known to spawn near the stables outside the city of Markarth and his dialogue remains as if he's near the abandoned house.
There is a Poltergeist reference when Tyranus decides to flee the house and get help. The table near the exit of the house has chairs stacked on it similar to a scene in the movie.
To fail this quest, refuse Molag Bal, and kill Logrolf in the pen
If the shrine holding the Mace is activated from the side or from behind, you will still be able to move around the room when talking to Molag Bal.
Activating the shrine from the side can sometimes get you stuck inside the spikes with your character clipping into the spikes, but not letting you out. This can cause some problems with the dialogue, as Molag Bal sometimes won't enter into direct conversation, but instead just start talking, causing him to continuously start the conversation over and over. Remedied by waiting or loading the auto-save.
Not responding to the priest outside of the house the first time you see him may make the quest unable to be started.
Door of house does not lock automatically and may lock after talking to Molag Bal. This traps you inside of the house which requires a key to open door. No fix known, revert to earlier save.
Upon striking Logrolf with the Mace, he may glitch out of the cage Molag Bal has erected for him. If this happens, it may become difficult to damage him enough to progress.
At random times, Tyranus will enter the house and then enter again. The problem with this is now he will continue to stand in the center of the first room instead of going deeper into the house. This will make the quest impossible to complete due to the basement needing a key to open and this effect can only removed by the Daedric Prince telling you to kill Tyranus. A way to force Tyranus to the basement is to hit him. Get him to attack, then run to the basement, once there kill him and the quest will progress.
An extension of the above bug, if you kill Tyranus while he stands in the center, but leave before going to the shrine in the basement, then your vision may be permanently red and hard to see with, and seemingly as impossible to fix as the above bug. This can be fixed by going to Shearpoint, after you've done the Dragon Rising quest, and killing the dragon there. This seems to fix the coloration.
Also, if you go to the basement without killing or hitting Tyranus, and wait for the shaking and discoloration to start, then leave, niether will go away.
The above glitch can be fixed by simply loading the auto-save.
Loading the autosave sometimes doesn't work.
Another way to fix your vision is to drink Sleeping Tree Sap. When the sap wears off your vision should return to normal.
Like this bug, sometimes Molag Bal's narration won't go away. It might get stuck on the screen and pretend to continue talking if you draw a weapon as he starts to say it. remedied by simply killing Tyranus, even though the quest doesn't say to. No bounty added.
If you pickpocket Tyranus and take everything he has he will not move deeper into the house. If you go into the basement and cause the house to start shaking and then go outside the entire world will also be affected and will shake mercilessly. Upon returning to the house you can kill him and speak to Molag Bal, but the front door will now require a key and you will be permanently trapped inside.
After you speak to Molag Bal you may have some trouble exiting the house (you require a key). If you have a saved game before you spoke to Molag Bal load it up, kill Tyranus and exit the house.
If you become trapped in the house because of one of the various bugs, but you have killed Grelod the Kind for the quest Innocence Lostand haven't slept yet, sleep in one of the beds. During your sleep, you will be kidnapped by Astrid to the Abandoned Shack and thus, you are no longer trapped in the house in Markarth.
If you arrive in Markarth via the drinking contest from "A Night to Remember", the innkeeper at Silver Blood Inn might not have the appropriate rumor and will never have the appropriate rumor to start this quest and Tyranus will never be outside the house or outside the city. Even using console commands to force start the quest or spawn a Tyranus does not work in this case. The cause of this bug is that the Forsworn conspiracy quest does not start properly, as it is supposed to start with a murder in the market as you enter the town for the first time through the main gate *** You MAY be able to fix this bug by going to the market, stealthing and killing Weylin while in stealth. If done correctly you will not get a bounty or be attacked and the other people will start yelling about the Forsworn attack, thus triggering the quest to proceed correctly. After you should be able to start the House of Horrors quest correctly as well.
There is also a bug that Molag Bal will not speak at all and you will have no instruction to further the quest, the best course of action is to just kill Vigilant Tyranus as you will be killing him anyway.
Stop the constant shaking by killing Tyranus and exiting the house without going to the altar, though there still may be problems with the visuals such as the gamma levels.
While beating Logrolf into submission he may pop out of the trap and stand outside of it. He is still unable to move and the quest is still completable.
While going back in the house it will say key required no fix known yet.
In some cases if you enter Markarth, Tyranus will follow you and try to kill you and you not be able to start the quest "The House of Horrors". To fix this, have Tyranus follow you out of Markarth, lead him away from the city gate, next beat and/or slash at him until he gets down on one knee (because at this point he is unkillable). While he's on one knee, quickly run back into Markarth (The Whirlwind Sprint shout should be helpful). Then when you come back out of Markarth, Tyranus should be where you left him except he should no longer be hostile. At this point you should be able to speak to him and begin "The House of Horrors" as you normally would. Another way to fix this bug is to use a spell of Calm or Voice of the Emperor, after which Tyranus should be non-hostile and allow the quest to begin.
360 PS3 Sometimes the trap is not triggered when you first try to take the mace and the quest does not continue. This is solved by using Telekinesis on the mace.
This can also be solved by using the disarm shout on the mace and then grabbing it.
It is possible to get stuck at the beginning of the quest. When Tyranus enters the house, if a guard sends you to jail, the door will be locked again after you come back.