A Dangerous Game
Prerequisite: Complete "A Poet Under Pressure." | Suggested Level: 12
You can also meet with Zoltan after the big rescue. He's got some debts to pay, and he plans to do that by selling rare Gwent cards. Head to your marker to find a door you can't get through. Instead, look to the ladder nearby and follow it to the roof. You'll be able to get into the house's second floor this way.
Inside, you'll find a dead body and some bandits. Take them out, then loot their bodies for the first card and the key to the front door. Loot the chest under the stairs for a ledger - this lists the buyers of the other two cards you need.
Return to Zoltan and ask about the other two buyers; he'll give you more information. Now you need to visit the first buyer, Caesar, so meet Zoltan at the man's house. After a cut scene, you'll be free to roam the house. Head to the second floor, check the book case, then check the nearby desk for a key. Use it on the hole in the bookcase to open a passage to the third floor, where you'll find the card you're looking for. Head back down to Zoltan, and some thugs will bust into the house. Take them out, then be on your way.
The last card is found on the bottom floor of the Golden Sturgeon in Harborside. You'll find yourself in quite the high stakes Gwent game when you arrive. Win, and the thugs will attack you. Take them out, get the last card as a reward, and return to Zoltan at the Rosemary and Thyme.
Now you'll have to accompany him as he sells the rare cards. Head to Putrid Grove to find the buyer dead at the hands of Duke and his men. Zoltan will take care of the ruffians, so chase after Duke up ladders, across walkways, and through sewers until you catch him. Deal with him as you'd like, and this long quest will end.
The Soldier Statuette
Prerequisite: Complete "A Dangerous Game." | Suggested Level: 14
During "A Dangerous Game," you can find a jade figurine on the upper floor of Caeasr's House. Pay Triss a visit at some point to inquire about it. She'll restore the object to its true form: a Nilfgaardian Soldier. This ends the short quest.
Gwent: Old Pals
Prerequisite: Complete "A Poet Under Pressure." | Suggested Level: N/A
You can also play Gwent against Zoltan after Dandelion's rescue. Beat him, and he'll mention Vernon Roche as an opponent. Beat him, and he'll recommend playing Lambert or Thaler. Beat both of these old friends to complete the quest.
Contract: Deadly Delights
Prerequisite: None | Suggested Level: 15
Check the Notice Board in Harborside to get this contract, then speak to the guard at the fish market to learn about a night patrol that got wiped out. Go talk to the medic that examined their corpses and ask him some questions about what happened.
This will send you to the spot where the bodies where found. Use your Witcher Senses to find a strange set of hoof-print tracks. Follow these to wind up outside Crippled Kate's, a brothel. Examine the perfume bottle nearby to get a scent, then follow the red mist to encounter a very dazed townsperson. After a talk with him, it's clear what you're dealing with here: a succubus.
To get inside her house, enter the neighboring one. Head to the second floor, climb the ladder, than scale the next ladder outside. This will let you drop right into her bedroom. Head down a floor and slay her, then return to the guard in the fish marker for a reward.