Travel to Morthal and speak to any guard about the burned house to start the quest. Now go and speak to the Jarl . Ask her about Hroggar’s house and then we need to go investigate the house, which was burned down to ashes.
Go there and speak to the ghost, Helgi. Time to play hide and seek with her. Wait for night to come (or fast forward time) and go directly west from the house to find a coffin and a vampire named Laelette . Kill the vampire and examine the coffin.
The little girl starts talking and explaining things. Wow! Now go and speak to Thonnir about Laelette. After discussing whether she was a vampire or not, its time to go to Alva’s house and see if she’s indeed a vampire. It’s easy to find once you enter the town, but you will probably need to lockpick the door to get inside (it’s just an Adept lock ).
If you go during the NIGHT, you will likely find Hroggar inside. He will of course attack you but you can kill him and get away with it. If you go during the DAY you can likely just head down to the cellar with no one seeing you. However, if you do go during the day, you can run into Alva, who is indeed a vampire, and you can kill her right then and there.
Either way, once inside, go to the cellar and pick up Alva’s Journal and read it. Now go to the Jarl and give her Alva’s Journal. She will read it too and then ask you to go kill the master vampire, Movarth .
Head oustisde and you’ll see all of the "warriors" the Jarl promised. Meh… Talk to Thonnir now who will scream " VENGEANCE !" and lead the group of people towards Movarth’s Lair to the northeast. Go ahead and follow them. At the lair the others will get queasy and leave, but talk to Thonnir who is more courageous than the others and ask him to follow you to gain him as a companion. Now enter the lair.
In this first room, kill both Frostbite Spiders from above then go to the bottom afterwards and continue. Kill the lone vampire that’s giving you his back sitting at the table. From here, go up the small path next to the table and kill another lone vampire (I found this vampire in a cubby to the upper right, but she moves so if you don’t see her she may be best saved for later).
From here, proceed north and then east. You can find a vampire thrall in a pit in this big room, but you can easily sneak up on him so kill him off and continue on. You’ll come to a ramp on the left you can access that leads into a big room with a dining table.
Keep following the ramp and if you’re sneaky you can use it to reach the northwest corner of this area. There’s a vampire guarding the hallway, but you can get the drop on him. There’s some bedrooms past the guard, one of which has an ILLUSION SKILLBOOK "2920, Sun’s Dawn, v2" on the nightstand.
You can find Morvarth’s Boots near the nightstand as well (as you can tell, Morvarth has a boot fetish). His personal boots have a sneaking enchantment on them that ups your sneaking by 15% by the way.
From here you can work your way southeast and sneak up on Movarth . Movarth himself is rather easy but if you’re at a higher level he can have some high level vampire help (like nightstalkers) so be sure to get some sneak attacks in. Kill all the vampires that help assist him as well.
Note: Vinheim found Alva in this cave, so there’s another location for her and one less enemy to worry about if you already killed her!
Now check the room southeast of where Movarth was to find a chest to loot as well as an alchemy table. The path south has another vampire (the patrolling one I mentioned earlier) and more loot for you. Leave and you’ll find Helgi’s ghost before leaving (what a nice touch!). Leave, return to the Jarl to get your reward, and this quest will be over.