The Battle of Kaer Morhen

The Battle of Kaer Morhen is the main quest where everything Geralt has been building towards finally collides. After the Isle of Mists, Geralt and Ciri retreat to the old witcher keep, and the Wild Hunt follows. Vesemir, Yennefer and Triss are waiting, and every ally recruited in the Brothers in Arms quests shows up to help, from Eskel and Lambert to Zoltan, Hjalmar, Roche, Ves, Keira and even Letho, if he is still alive and was invited.

The council

Before the fighting starts, everyone gathers in the main hall to plan the defence. Geralt makes two decisions: use the laboratory for potions or for witcher traps, and use the workshop to patch up the walls or clear out the armoury. The potions give Superior Swallow, Thunderbolt and a runestone, while the armoury gives the silver sword Rose of Shaerrawed. Taking the time to walk around beforehand is worth it: the conversations with Ciri and the others are some of the warmest moments in the game.

The battle

The fight starts in the woods, where Geralt and Lambert close three portals with Yrden or dimeritium bombs before Imlerith appears. From there it becomes a race back to the keep, a fight to close the main gate, and a desperate retreat as Yennefer’s barrier fails and the White Frost creeps in. Ciri gets her own playable moments, helping Triss on the walls and saving Eskel from the navigator Caranthir.

The cost

In the end, the Hunt breaks through and freezes almost everyone. Vesemir protects Ciri as long as he can and, in one last act of defiance, stabs Imlerith with a dagger. It costs him his life. Ciri’s grief unleashes her power in a scream that tears through the Hunt, Caranthir opens a portal to pull Eredin away, and Avallac’h arrives just in time to stop her from harming her own friends. The quest ends with Vesemir’s funeral pyre, and Ciri taking his wolf medallion before she decides to stop running.

Walkthrough

Talk to Vesemir, Yennefer and Triss, then optionally walk around Kaer Morhen and speak to your allies. Fast travel and Roach are disabled.
Join the council in the main hall. Choose potions or traps for the laboratory, and wall repairs or the armoury for the workshop.
Prepare your gear: this is the last chance to use your stash for a long while.
In the woods, close three portals with Yrden or dimeritium bombs while fighting Wild Hunt warriors and hounds.
Ride back to the keep, close the main gate with the lever, and help Lambert if Keira is not there to save him.
Retreat through the courtyards ahead of the White Frost. As Ciri, help Triss and Eskel against Caranthir, then open the gate.
As Geralt, close the remaining portals and reach Triss to trigger the final cutscene.

Quest Consequences & Choices

Vesemir always dies at the end of the battle, killed after he stabs Imlerith to protect Ciri. Lambert can also die if nobody saves him during the battle, which is why recruiting Keira Metz matters. Your council choices only decide which rewards you get and how many enemies come through the walls. The quest leads straight into Blood on the Battlefield.