Vigilant Tyranus

 is a Witchhunter dedicated to driving off Daedra and their cults of followers. The Dragonborn finds him in Markarth, outside the Abandoned House.

Interactions
Tyranus asks the Dragonborn to help him while he investigates a possible Daedric Cult in an Abandoned House. During the raid, objects float across the room, apparently moving by some sort of a mystical force. A disembodied voice tells the Dragonborn to kill Tyranus. If they do not respond, Tyranus is driven mad by the disembodied voice and attacks the Dragonborn.

Quests

 * House of Horrors

Bugs

 * Tyranus may sometimes attack on sight. This is caused by eventually having Daedric artifacts or such in your inventory whilst walking near him. The Markarth guard may or may not attack Tyranus until he takes a knee: he cannot be killed. Violent retaliation by the Dragonborn is not considered a crime; however, Tyranus will not desist until the Dragonborn leaves Markarth via the City gate, and gets far enough away from him to break the chase.
 * This can sometimes be remedied by entering the Temple of Dibella's Inner Sanctum.
 * Tyranus may sometimes never stand outside The Abandoned House because of a glitch in the game. This can sometimes be fixed by leaving the city via the gate and then going back inside. Another problem is that he can be stuck on the stairs right outside the city gate.
 * This can be fixed by the Dragonborn talking to Tyranus and initiate the quest " House of horrors " and he will enter the city.

Also, if you attack Tyranus, then sometimes the quest will go into the completed section, saying Tyranus is dead and the quest failed, even if he is in front of you talking.

If you can't find Vigilant Tyranus, you can go to the Silver-Blood Inn and ask the tender about rumors and he will point you in the right direction.