By The Gods Stringing Up Sods main quest starts when you reach the city of Flotsam during the first Witcher 2 Assassins of Kings Enhanced Edition act.
After you escape Iorveths archers on the beach, you will talk to a guard who informs you that an execution takes place in the city, and everyone is heading to the town square.
You should see who is going to be killed as soon as you enter the city.
Cultural events are rare in the province. Thus it is surprising that when a rarity like the hanging of collaborators takes place, the whole town turns out.
And when in Nilfgaard, do as Nilfgaardians do. Geralt and company proceeded without hesitation to the scaffold square to partake in the local entertainment.
Enter the city through the front gate, after you gather all resources in the vicinity. You will find yourself in the Craftsman District. Continue towards the town center (North) and approach the scaffold, to trigger a new cutscene.
Looks like Zoltan and Dandelion (Roches informant) will be hanged soon. Notice that Roche asks you to avoid a killing. Get ready for a fistfight and talk to the guard near the scaffold (the one wearing armor).
You will find out that Zoltan is accused for conspiring with the Scoiatael elves while Dandelion is corrupted. During the second phase of the dialogue you have two options:
Option 1: “People, is this justice as you see it?” You will incite the angry mob, and start a fistfight.
Option 2: “Ive heard enough bunk. Out of my way.” A fistfight sequence starts.
After you complete the sequence, you will head up the scaffold and stop the executioner by wining another fistfight.
The cutscene continues and Loredo shows up, telling you that Dandelion burned a tower. Two of the prisoners will unfortunately die by Loredos hand, who will set Dandelion and Zoltan free.
At the end of the dialogue, Loredo asks you to see him at dawn (Indecent Proposal main-quest starts now), while Dandelion and Zoltan want to celebrate with you at the tavern.
The inn is near the scaffold, to the left, while facing the dead prisoners. Next to the entrance you should see a board, and on it some notices. Make sure you enter the tavern after you pick up all notices: Endrega Contract, Nekker Contract, Proclamation of Pardon for Dimitri, Cedrics Notice and the Troll Contract.
You should focus on them as soon as you finish By The Gods Stringing Up Sods main quest and A Sword for Monsters.
Note: Keep in mind that you need your silver sword if you want to kill the monsters for the side-quests you started.
For now, head towards the tavern and talk to Loredo, Zoltan and Roche to finish the main quest. Tell them what happened and during the conversation a new cutscene starts showing a beast attacking the harbor. As you travel to the docks, speak to the villagers for additional information regarding the beast known as the Kayran.
You can persuade them to leave or you can threaten them. It is a good idea to avoid a direct fight and continue your dialogue with the sorceress (Sile de Tansarville) and Triss. Two additional quests will be added to your journal: The Kayran and The Kayran: A Matter of Price.
Note: At this point By The Gods Stringing Up Sods ends and you can start The Kayran main-quest, Indecent Proposal or any other side-quest from your journal, but it is wise to prepare yourself and recover your Silver Sword which is the goal of the side-quest called: A Sword for Monsters.