Vengeance is a Main Quest in Kingdom Come Deliverance (KCD) that stays with you throughout the game. It starts automatically when accepting the 5th main quest “Train Hard, Fight Easy“.
You’ll notice there are no objective markers (quest markers) for it. This is for a simple reason: all the objectives are completed automatically throughout the story.
Basically, Vengeance is your main task, the reason why you play all the main quests. The reason why you do anything is to avenge the death of your parents and punish Markvart von Aulitz, the one responsible for their death.
Long story short, just play the main story line and this quest auto-completes at the end. There’s nothing more to it.
However, it’s also a weird quest because you can’t actually get your father’s word back, nor will you ever get to kill Markvart von Aulitz. You’ll never even encounter him in person (he is only shown in one cutscene during the first main quest).
You’ll kill runt automatically in the 14th main quest “Baptism of Fire“.
Find Markvart von Aulitz and avenge your parents / Get father’s sword back
Complete the 29th main quest “Epilogue“. However, there is no “real” way to kill Markvart von Aulitz nor will you get the sword back. Maybe we’ll learn more in a future expansion but for now there’s no way to actually kill Markvart von Aulitz. He disappears from the map after his cutscene in the first main quest.
Just finish the Epilogue and the Vengeance quest will conclude, thus also unlocking The End trophy / achievement for completing the main story line.
Next Up: Epilogue Main Quest
For more Walkthroughs, check out the full Kingdom Come Deliverance Walkthrough (All Main Quests).