Vergen Besieged is a main quest in Chapter II of The Witcher 2: Assassins of Kings.
This quest automatically begins after you lift the curse, all the shops and craftsmen become unavailable so it is advisable to finish up last minute shopping and crafting before going into the mist the last time. You begin in Philippa's quarters and you need to go talk to Zoltan at the front gate of Vergen. If you spared the trolls' lives, they will appear to help you defend Vergen (although it does not affect the outcome nor do you have more than the most fleeting opportunity to see the trolls in action). After a short cutscene you are given the task to open the hot oil valves. Go up the stairs and go straight for the mechanism between the second and third oil reserves. The enemies that are here never run out so don't bother clearing them out.
After another cutscene retreat to the second gate and defend the walls. Several waves of soldiers climb up the wall. They don't put up much of a fight since you will have allies to distract them. After finishing off the enemies follow Saskia down to the mines. Kill three mercenaries in the first room, another four mercenaries in the next room, three rotfiends, then after a cutscene you are faced with six soldiers and a mage. The mage can teleport around the battlefield and can cast Quen II and lightning. You can leave the soldiers to Saskia and focus on the mage. When you get the mage's life to less than half another cutscene will happen where you learn something about Saskia.
Afterwards go back to the walls. Follow Zoltan as he closes the gate. Then defend the walls again in exactly the same fashion as before. Another cutscene completes the battle.
Following the battle, Henselt surrenders and negotiates with Saskia.
Geralt and Iorveth can follow Philippa, but she eludes them in the end, taking Saskia with her.
- Geralt awoke in Philippa Eilhart's quarters right in time. Henselt's forces were approaching Vergen to besiege the town. There were precious few heroes who could tilt the battle in Saskia's favor around, so the witcher had no other choice but to get out of bed and take matters in his own hands. Zoltan Chivay awaited him at the gate.
- And so the assault began. The very first wave of attackers could destroy the barricade and break through into Vergen proper. To weaken their resolve, Geralt and Zoltan decided to activate an old dwarven mechanism and pour boiling oil on the attackers. Zoltan ran for the cauldrons on the left, and Geralt hastened to the lever on the right side of the walls.
- With the skill of a consummate engineer, the witcher activated the mechanism on the walls, and boiling oil rained down on the enemy. This would not stop the Kaedwenis completely, but it did thin their numbers and weaken their resolve. The deed done, Geralt raced back to the defenders. Zoltan was waiting for him near the gate.
- If only conventional weapons were used during the battle, the attackers would be in for it. But there was a sorcerer on their side. Dethmold blasted the barricade to bits with his spells, the Kaedweni attacked, and the Aedirnians had to retreat.
- In a bold move, Henselt's soldiers attacked the walls. Geralt was in the first line, to repel them.
- The witcher didn't have a moment for respite. A second assault came after the first one, and he had to stand firm on his station once more.
- Henselt has been slapped on the wrist and was licking his wounds. However, that which could not be taken directly could be taken using guile. A secret passage was leading to Vergen, and Saskia was afraid the enemy might find it. Geralt ran to check out the underground corridor.
- Accompanied by Saskia, Geralt descended into the secret Tunnels of the Founders. The defenders suspected that the enemy could use the corridors to launch a treacherous attack from behind. Their suspicions proved correct, for the expedition first encountered Kaedweni soldiers, and then Dethmold himself, led by a Vergeni traitor. Geralt could not let this opportunity pass and lunged at the sorcerer, sword in hand.
- Yet Dethmold was no fool and would not stand by idly to be sliced by the witcher's blade. He fell back to a safe position and attacked Geralt with a spell so malignant that our hero's vision grew dark. Defeated, the witcher fell to the ground. The dwarven corridors would have been his grave if not for Saskia. The Dragonslayer shape shifted, transforming into a dragon, and lunged at Dethmold, causing him to flee. Thus, the witcher learned Saskia's secret. Suddenly, the many vague elements of her story began to make sense. It was clear it had been made up from the start. The Dragonslayer, being a dragon herself, had used the story to hsape her image as a fighter for a free Pontar Valley, and to hide from humans her rather inconvenient true form. The witcher, who had miraculously survived, had little time to analyze matters in detail. He had to return to the walls and save Vergen!
- In the meantime, the Kaedweni mounted a third assault, putting all their forces on the attack. Geralt realized the defenders won't hold for long, but he was determined to fight to the bitter end.
- Just as defeat loomed inevitably over the defenders, Iorveth returned to Vergen, leading reinforcements with him. The unexpected relief bolstered Saskia's soldiers and they began to cheer. Geralt was as happy as the next man, but he controlled his euphoria. He instantly realized that a great opportunity would be wasted unless he broke through to the elven leader and joined forces with him.
- Geralt and Zoltan reached Iorveth. Now, to trap the Kaedwenis in the town courtyard, they needed to close the gate. To unblock the gate mechanism, the dwarf had to hit the lever with all the strength he could muster.
- Closing the gate reversed the course of the battle. The Aedirnians found new strength, putting Henselt on the defensive and finally forcing him to surrender. Thus ended the war of Upper Aedirn.
- The negotiations with Henselt came to an end. The Aedirnian victory was sealed. Yet, instead of celebrating the victory, Philippa and Saskia left in a hurry, without giving an explanation. If you suspect that they had reasons for such behavior, you're right. If you also think that the witcher managed to meet them before the left Vergen, you're also correct. Geralt and Iorveth followed them.
- Philippa and Saskia disappeared in a portal without a word of explanation. Geralt decided to search Philippa's quarters, hoping he would find any clues.
- While searching Philippa Eilhart's quarters, Geralt and Iorveth found a book tellingly titled "Venoms and Poisons". It was dog-eared at a page describing a poison allowing one to control another's mind. This was not irrefutable evidence, but it did cause certain suspicions that had been forming in our her's mind to sprout like beanstalks that wrap around poles in Dol Blathanna. Philippa had not only feigned being the Dragonslayer's friend. While treating her, she had poured her own venom into Saskia, a venom that affected the mind, not the body. In brief, the sorceress had taken control of the dragon's mind. Knowing Philippa, Geralt knew that Lady Eilhart would not hesitate to use her new weapon. So the witcher and Iorveth conferred and agreed to save Saskia.
- Among Philippa Eilhart’s abandoned possessions, Geralt learned a shocking truth. It turned out it was the sorceress that poisoned the Dragonslayer! Our hero had no idea what caused her to do so. But he guessed his finding was a trail of a bigger intrigue and saw all the previous mysteries in a new light. Vergen was triumphant, yet unaware of the heroic Saskia’s disappearance, and Geralt and Iorveth began their search. The witcher was entering the final chapter of the story of the assassins of kings.