Now or Never - Novigrad
Location: Vegelbud Residence & Novigrad
Quest Giver: Automatically accepted after completing A Matter of Life and Death
Other Requirements: This quest must be completed before The Isle of Mists Story Quest
This quest automatically begins after completing A Matter of Life and Death, the first quest Triss gives you as part of her story line. When you arrive in Novigrad to see Triss she will be trying to decide whether or not to risk her life to save Berthold and Anisse; you'll be able to choose whether or not you wish to help these two and choosing to do so will change the first part of this quest. If you choose not to help them then you'll basically be able to skip ahead to where you go to the Kingfisher Inn.
Note: If you choose to help the two mages then a man named Oliver at the Kingfisher Inn will end up dead. If you choose not to help the two mages then they both will die but Oliver lives.
(If you decide to save Berthold and Anisse) Follow Triss until you reach the house with both of the mages. Along the way Triss will stop you and tell you to wait for a patrol to pass - you can engage them if you want, there is no penalty for ignoring Triss. When you arrive at the house with the two mages you'll have to use Axii on them to get them to listen.
Now both paths will converge and you'll have to make your way to the Kingfisher Inn. When you arrive there will be some guards inside and Oliver will be dead, if you helped the two mages. Otherwise there will be no one here and Oliver will be alive, as aforementioned.
You'll get a scene in the basement of the Kingfisher Inn with Triss and Dijkstra. Once the scene is over and you regain control of Geralt you'll need to clear the sewers of enemies with Triss. When you reach a dead end in the sewers use your Witcher Senses to locate a wall that you're able to Aard down. It'll lead you to a library with a ton of books for you to grab before leading you back into the sewers, to an area with a lot of rats.
Tip: If Triss doesn't follow you through the sewers try interacting/speaking with her to get to to follow.
For the most part the sewers will be straight forward, protect Triss during any of the fights down here even though I don't think she can die. You'll reach a large room with a bunch of rats - use Igni and Whirl (if you have it) to easily clear a path through. After this room you will have a few more rooms to travel through before you encounter a Katakan (pictured above).
It'll be a really easy fight - he's like every other vampire you've fought up until this point. When you arrive at the docks there will be another scene followed by an attack by the Witch Hunters. After you finish off the Witch Hunters you'll have the final dialogue scene of this quest - during which you can romance Triss. Choose the options that encourage her to stay and tell her you want a second chance or that you love her. Selecting the right choices will get her to stay with you in Novigrad.
Upon completion of this quest Dijkstra will approach you after this quest and fill you in on his plan which will give you the follow up quest, A Deadly Plot. I'd highly recommend you complete the next quest in the chain too as it's one of the quests you need to finish to unlock Reason of State, one of the few side quests you can complete that will change the game's ending.
Completion of this quest will also allow you to ask Triss for help in a major future story quest. For more information about this head over to my Brothers In Arms: Novigrad Quest Walkthrough.