Carnal Sins - Novigrad
Quest Giver: Automatically starts after Cabaret
Other Requirements: N/A
You'll begin this quest immediately following your completion of the Cabaret Quest. When you begin this quest you'll be given the option of fast traveling to the sewers with Joachim von Gratz (the surgeon) or meeting him there at a later time.
Inside the sewers you'll have to fight some Drowners and a Water Hag - it's a brief trip to the morgue. Once in the morgue you'll find the dwarf's corpse in the northeastern most portion. I recommend you spend some time running around gathering everything inside before inspecting the body.
When you finish inspecting the body you'll be thrown out of the morgue and your quest will update again, giving you three locations to visit in Novigrad. All three are marked on your map and you can change which objective you'd like to track by going into your quest log.
Here are the three objectives you have to complete before advancing the quest:
Corpse collector: Use Axii or pay him for the information you want; then punch his ass in the face.
Alley where Priscilla was attacked: When you arrive one of Priscilla's friends will have three towns folk-thugs attack you. Beat them up using your fists then you'll get a short cutscene. Once that's finished examine the foot prints, crate and other clues in the alley to update the quest. There is also a Concerned Citizen's Letter for you to find on the wall.
Woodcutter's House: When you first arrive you'll have a scene where a messengers tells you there has been another victim. After the scene, knock on the large double doors for access to the courtyard and to talk to the deceased's brother. You'll have to explore both the courtyard and the building for all of the clues.
Once you're done with all three locations it's time to return to the coroner. The spot you have to go is marked on your map so zip on over to there and have a chat with him. During the autopsy you'll discover a letter which marks the next person who is going to be killed, Patricia Vegelbud.
Now you have to head on over to the Vegelbud Residence and ask to see Patricia, there will be some dialogue and scenes after which you'll have to pursue the killer. You will eventually lose track of him and will have to fight some Vegelbud Guards. There'll be some scenes after which you'll learn of the next person on the killer's list.
As you could probably already guess, our next destination is Crippled Kate's, it'll be marked on your map so head on over there. When you arrive you'll interrupt Nathaniel while he is torturing a girl. I highly recommend not killing him (which means don't provoke him) as you'll quickly learn this is not the man we're looking for.
Pick options 2 or 3 and you'll learn that the man before you, while clearly fucked in the head, is not the person you're looking for. He'll tell you the true killer, the coroner - who you will find at the docks. When you arrive the coroner will reveal his true form to you, he's actually a vampire!
Katakan/Vampire Weaknesses: Vampire Oil, Igni
Take him out then return to Dandelion to complete the quest. This ends the chain of quests as well.