After agreeing to help both Liam and Matilda, they will give Wine Wars: Coronata and Wine Wars: Vermentino, respectively. While each one has 5 tasks, there's only one location at each you need to visit to start this one.
For Vermentino, you need to go to the guarded treasure northeast of the Sansretour valley signpost. Once the archespores are dealt with, search around until you find the body with a heavy brass key and a letter on elegant stationary. Read the note to learn someone is sabotaging the vineyard.
For Coronata, go to the guarded treasure northeast of Coronata and south of the Trading Post. Take out the archespores, then once more search the bodies, this time finding orders on elegant stationery. Read it to learn of a location far south, to the east of Tesham Mutna Ruins. Note that the path splits here depending on the timing.
If you investigate the location before turning in one of the quests: Once there, enter the cellar and head into the lower area to fight an archespore. Once it's cleared out, examine the seedlings nearby, which Geralt will note he should destroy before they hatch so use Igni on them. If you don't destroy them and turn in the quest, if you ever visit the cellar again, one will have hatched and will attack.
Also look for the lootable crate near the seedlings for the stocktaking report. This will point out the true saboteur and Geralt will turn in the information to the clerk and this will make Liam and Matilda decided to join operations. If you haven't yet finished their individual tasks, they will then be combined into one, Wine Wars: Consorting.
If you investigate after turning in one of the quests: Once there, enter the cellar and head into the lower area to fight an archespore. Once it's cleared out, examine the dead body to find Fragment of a letter. However, there's no incriminating evidence by this point to figure out who was really behind the sabotage.
- From the start, both Matilda and Liam insisted the problems at their vineyards had not appeared out of thin air. Naturally, they accused one another of foul play. Geralt suspected there was more to the matter, and yet again his intuition proved true. While solving the problems at the vineyards, he had happened on some notes. These suggested someone had intentionally planted archespores amidst the vines at both estates. The witcher had also found a key to the shelter where saplings of the beastly plants had been stored.
- If Geralt didn't investigate until after starting the second part of Wine Wars: Belgaard:
- The dugout was almost completely empty. At any rate, the witcher found nothing to help identify the individual behind the sabotage at Coronata and Vermentino. The mystery remained unsolved.
- If Geralt completes the investigation before finishing Wine Wars: Belgaard:
- Geralt searched the dugout and learned that the sabotage at Coronata and Vermentino had been the brainchild of Count Vladimir Crespi.
- What Geralt had learned shed new light on the dispute Liam and Matilda. It seemed Count Crespi had intentionally incited the quarrel between them. They decided to do him one better - Liam and Matilda settled their differences and formed a consortium.
- Find the place mentioned in the letter.
- Search the warehouse using your Witcher Senses.
- Defeat the archespore.
- Read the mysterious letter.
If Geralt investigated before the second part of Belgaard: