Witch hunters, you say? Best cut them down, I say.
The Witcher 3: Forefather’s Eve
Once you’ve completed A Tower Full of Mice, go out of Keira’s hut and you’ll find the peller. If you haven’t completed the Family Matters main quest you should work through that before attempting this.
Get over to Fyke Isle and meditate until midnight when you can speak to the peller. At this point you’ll have to protect the villagers from the Drowners and Water Hag, so fight quickly and efficiently.
You now need to make a decision – help the pellar and fight the witch hunters, or avoid the fight altogether. If you walk away the quest is over.
When the ritual is interrupted you’ll face three Wraiths so use the Yrden sign to trap them in place. You now need to get over to the next marker, which is near the Orphans of Crookback Bog signpost.
At the highlighted area fight off the Rotfiends first, then find the body using your Witcher senses. Burn it with the Igni sign and then fast travel back to Heatherton to meet up with the peller and complete the quest.