Important: while this quest will fail if you haven't completed it by the time you begin the council in The Battle of Kaer Morhen, the actual cutoff point is The Isle of Mists, as Vesemir can't be interacted with after it's started. However, if you manually go to the cave before the council, you can still complete the quest successfully, even after the The Isle of Mists quest is completed.
You will find Berengar's notes near western wall of Kaer Morhen. After reading them Geralt will decide it's best to consult Vesemir, so do just that. Vesemir will tell Geralt a story on how Berengar tried to craft the sword, but lost the diagram during the fight with a Chort he had to retreat from. After that he will tell Geralt where is the cave the fight took place. As Vesemir tells you the best way to reach it is by the river. Once there the quest will update and you can start exploring the cave. Eventually you will reach the Chort and be forced to fight it, once dead you can search the rest of the cave and you will find the diagram inside a bag and the quest completes.
- In one of the now-unused bedrooms of Kaer Morhen Geralt found a note left by Berengar, a witcher who had once been his companion and colleague. The note indicated Berengar had been working on forging an exceptional sword called Tor'haerne. The note was sparing in its details, so Geralt decided to ask Vesemir if he knew something more on the subject.
- The elder witcher told Geralt the story of how Berengar had tried to forge a silver sword with extraordinary characteristics. All his attempts, however, went awry and he lost the diagram while trekking downriver to kill a chort.
- Geralt finished what Berengar had started: he followed the same route, killed the monster and retrieved the Tor'haerne diagram.
- Find Berengar's notes in a chest in the western part of Kaer Morhen, to the west of the grindstone in the 2nd courtyard.
- Read the notes.
- Talk to Vesemir.
- Explore the cave using your Witcher Senses.
- Kill the chort.
- Look for the Tor'haerne diagram, for a relic silver sword, in the cave using your Witcher Senses.
- Despite it taking place only in Kaer Morhen, the quest log shows the "multiple locations" icon.
- This is the same cave you go to for Scavenger Hunt: Wolf School Gear Upgrade Diagrams - Part 4 to find the Superior Wolven boots diagram.
- If you already have the Tor'haerne diagram the quest will not start. Talking to Vesemir doesn't give you any options to further progress the quest.