Arrow-Head is a unique and highly missable task in the 
Kuttenberg region of Kingdom Come: Deliverance 2. Start it directly after you finish the main quest Speak of the Devil and return to 
Devil's Den.
If you wait too long or progress significantly into the next main quest, the encounter may no longer appear, and you can lose the chance to complete this task.
Arrow-Head quest location
This task is very short, but also highly missable and time-sensitive. It only becomes available after completing the main quest 
Speak of the Devil.
To trigger the quest, travel the road between Devil's Den and Grund shortly after that main mission ends.
More precisely, follow the road east of Devil's Den, the one with the river stream crossing it. Follow it until you reach a man asking for help on the left side: Karel Arrowhead.
Meet Karel Arrowhead
Talk to him and learn that Karel Arrowhead is a bandit leader who famously survived being shot in the forehead by one of his own men. The arrow remains lodged in his skull, giving him his nickname and a reputation as a man protected by divine forces.
Karel will ask for your assistance in carrying the second heavy sack back to his nearby camp. In the sacks is charcoal he has recently stolen, as he will admit if you ask him further.
Carry the cargo
Karel will pick up one sack, and you must pick up the other one remaining on the ground.
Follow Karel as he leads you through the woods toward his encampment.
You can engage him in conversation during the walk. Karel has a lot of interesting dialogue and thinks of himself as a human touched by good and some kind of medieval Robin Hood. He is keen to share a lot of information about his “magical” arrow and his outlook on life in the wilderness with his bandit group.
Rewards and next steps
Once you reach the bandit camp north of Grund, follow Karel to the designated drop-off point and put down your sack. Speak with him one last time to conclude the task.
Karel will grant you a full 7 Groschen for your manual labor.
Completing this task unlocks 
The Magic Arrow side quest in due course, but it is not immediately available.
Next: The Magic Arrow, Into the Underworld, or The Devil's Pack.
Arrow-Head FAQ
When should you start Arrow-Head?
Right after Speak of the Devil and your return to Devil's Den. Delaying risks missing the road encounter.
Where is the trigger on the map?
On the road from Devil's Den to Grund, east along the stream crossing, until Karel appears on the left.
What is the reward?
7 Groschen. The task also sets up The Magic Arrow for later.
Can you fail Arrow-Head by waiting?
Yes. Advancing other main content first can remove the encounter. Treat it as urgent if you want 100% tasks.
What main quests pair with this timing?
The Devil's Pack and Into the Underworld open after Speak of the Devil; do Arrow-Head before you advance too far.