Open Sesame - Toussaint (Blood and Wine)
This quest begins immediately after you complete Evil's Soft First Touches, the first story quest of the Hearts of Stone Expansion. For the first part of this quest you'll need to travel to Oxenfurt Auction House where you'll have a scene with the guards out front when you approach.
Vimme Vivaldi will interrupt your conversation and take you inside. Follow him upstairs for another scene after which you'll have an optional part of the quest involving meeting his friends. Below is a quick list of each person you can meet and what to do/what they offer.
Painter: Choose the Merchant Painting - tip about buying the van Rogh painting and selling it to Marcus TK Hodgson in Novigrad
Hilbert(Gwent): Play and beat him in Gwent for the Gaunter O'Dimm Card
Mignole: This lady is the most important one to talk to. She sells the patterns for Viper School Gear, a new set of Witcher Gear added in the Hearts of Stone expansion that can only be acquired here.
You have the option of learning more about Mignole's past as well if you agree to help her find her earring on the balcony.
Once you've talked to everyone the story will advance automatically, otherwise you'll have to sit and wait. During the auction there will be three items in total that you're able to bid on, it's recommended that you purchase at least the eagle statue and the painting.
Here's a list of the three items and what they're useful for/what they do:
Count Romilly's Figurine (eagle statue): Starts the A Dark Legacy Side Quest
Starry Night Over The Pontar (Painting): Starts the Avid Collector Side Quest
Pair of Spectacles (Glasses): These are a vanity item, Geralt can put them on using the accessories button.
When the Auction is all over Vimme will introduce you to the fine owner of this establishment, Horst Borsodi. No matter how you converse with him you'll end up thrown out of the building at the end and you'll have to fight the two people who tossed you out. Beat them up and you'll get a scene with a man known as "The Stranger".
There will be some dialogue after which he'll ask you to meet him at the Herbalists' House northeast of Oxenfurt. When you arrive there will be three guards here which you'll need to dispatch, after you do speak with the Herbalist about the yarrow extract and he'll take you to meet "the stranger".
Speak with the stranger for quite a bit of dialogue after which Geralt will accept 3 new mini quests that need to be completed in order to advance this quest any further. The 3 quests you accept are as follows:
You can complete these three quests in any order you choose. Once they're all done you'll have the option of fast traveling back to The Herbalists hut or meeting up with everyone here when you feel like it. There will be a long scene and a bit of dialogue before you're able to proceed with the mission.
When you finally regain control of Geralt you'll be inside of an attic and equipped with a Wooden Sword and a Mask. Go downstairs for a fight with a group of guards and there will be another scene afterwards. During the dialogue of this scene you'll have to give quick timed responses; failure to answer correctly will result in the guards attacking you.
1. Pull back from the auction house
2. Tell me a joke
3. Actually kinda funny...
Note: If you chose Casimir as your partner then when he blows open the vault it'll trigger a fight with the guards anyway, what you answer doesn't really matter.
Once you make it to the vault you'll have more dialogue and this time you're going to have to choose who you want to side with. Horst and his brother Ewald are your two options here as the game will not let you play a neutral role. Don't forget that the person you chose as your safecracker will choose a side as well. Here are the two safecrackers and the choices they make:
Casimir will side with Ewald
Quinto will side with Horst
What this means is if you have Casimir with you and you side with Horst, you'll have to fight Casimir and Ewald. If you have Quinto with you and you side with Ewald you'll have to fight Horst, the guards and Quinto. Once this situation is settled and you go to collect your loot, if you chose to side with Ewald he'll want to fight you over the loot.
If you take a more diplomatic approach Geralt will explain he doesn't need the will, just the box and this will settle things non violently. Once you've made your decision be sure to loot the entire vault before leaving. There is some unique loot here such as Diagram: Viper Venomous Steel Sword.
To proceed with the quest, follow the quest marker through the tunnel and out of the auction house. You'll find yourself back in Oxenfurt with the only quest objective left involving speaking with Olgierd. Head on over to the Alchemy to speak with him and complete this quest. If you have already completed Dead Man's Party then you'll receive the next quest in the chain, Scenes From a Marriage.