All hell breaks loose and it seems Eredin wasn't lying about Avallac'h, apparently a Conjunction of the Spheres has started, after a short conversation Geralt will be following Yennefer. You will have to run a bit so it's a perfect time to drink a Werewolf decoction, soon you will reach some horses you can ride on so best to use Nekker warrior decoction so the horse won't knock you off, as monsters will be spawning everywhere. Once you get close to Tor Gvalch'ca you will leave the horses and start climbing. Yen will create a shield to protect you from the White Frost. When you get close to the tower there will be a barrier preventing you from entering, however Yen will be able to make a hole in it for Geralt to get through it. Once there keep going, when you reach Avallac'h he will pull out his sword and then throw it down. As it turns out he did not betray Geralt and all of this was Ciri's idea as she intends to face the White Frost. Now you will have several dialog options, however no matter what you say she will go anyway so it's probably best to wish her good luck.
Note: Depending on your interactions with Ciri in the previous quests she will survive or not. And the following quest will be different depending on how it plays out.
- Eredin's words rang in Geralt's ears. Could Avallac'h truly have betrayed them? Could Ciri still be in danger, even with the Wild Hunt destroyed once and for all? Without a moment to lose and paying no heed to their wounds or exhaustion, Geralt and Yennefer plunged back into the post-battle chaos ravaging Undvik.
- It turned out that, while Avallac'h had not been entirely honest with the witcher, he was no traitor. Ciri had slipped off with him during the battle of her volition in order to - and please pardon the grandiosity, dear reader - save the world. She was convinced Geralt would never allow her to embark on this mad endeavor, and so decided she had to operate behind his back. All his promises and threats were for naught - there was no stopping Ciri once she'd made her mind up. The witcher could only watch as she stepped into the elven tower - and hope she would return safe and sound.
- Follow Yennefer.
- Get to the elven tower.