Ciri - Payback
To start this quest you'll need to speak with Ciri who is found in the Gildorf portion of Novigrad (up north, southeast of St Gregory's Bridge Signpost). Payback can only be started during the daylight hours as well, if it's night just meditate until at least 7-8am when Ciri will be shopping here.
How this quest works is you're going to have to follow Ciri around Novigrad and meet each of the people that helped her during her journey. This entire quest is fairly linear and you'll be following Ciri around from place to place and watching scenes. The first person you'll be visiting is Whoreson Junior and the quest will change slightly depending on which option you chose earlier in the game.
Killing him will result in Dudu the doppler taking his place; leaving him alive means he'll be a beggar on the streets. Once you're done with the dialogue here you'll have to follow Ciri to the Golden Sturgeon. You'll be meeting Bea here, there will be a little bit of dialogue and maybe a fight after which you're off to the last people who helped Ciri out - the circus!
You will have the option of participating in a horse race at the circus, it's totally optional to do this and there is no reward for winning or losing. When the horse race is finished or you've declined it altogether you'll have it'll skip to night time and there will be some more dialogue with Geralt, Ciri and the elves.
Aegar will approach you during the night and ask you and Ciri to steal some horses with him. You should agree to this as it'll give you a better ending to the quest - declining to help will cause a fist fight and you'll end up back in the Rosemary and Thyme with the quest ending.
Once you've agreed to help steal the horses you'll find yourself in Novigrad outside of some stables. Climb the scaffolding in front of you (pictured above) and go across to the wooden platform where you can get inside the building. Climb down the ladder in the building and steal the key from the table across from the guard and use it to open the stable door.
If you drop down instead of using the ladder or run at any point in here you'll wake up the guard and have to fist fight him. You'll also have to use Axii on 3 horses to calm them down, after you accomplish all of this you'll get a scene and the quest will conclude afterwards.