The Truce achievement requires you to resolve the conflict between the villages peacefully during the 
Battle of Frogs and Mice.
Frogs and Mice Questline & Truce Achievement Plan
Frogs can be started at 
Zhelejov at any time and Mice at Tachov is mostly available too, except for some instances when having Frogs in progress. The quests represent a series of tasks for each village and involve pranking their neighbouring enemies - it is obvious they have a lot of shared history together.
It is very easy to fail these quests and never even get to any of the endings. You only need to finish one of these quests for the Battle of Frogs and Mice to become available. After the quest becomes available, you can talk to Troskowitz Bailiff and then investigate the pasture for a quick resolution and the Truce achievement.
Do every task quietly without killing anyone and never report Olbram or Prochek to the other side. Snitching will fail one of the quests and on most instances prevent the achievement. If you get caught while destroying the laundry with sheep in Tachov, you can switch sites without punishment and we recommend doing exactly this to see the most of both Mice and Frogs and still get the elusive Truce achievement.
The safest order is to complete Frogs first, then start Mice, so follow this guide section by section.
Frogs
This quest is given by Old Olbram in Zhelejov and has two separate phases.
Steal the Maypole
Your first task is stealing the maypole from Tachov.
The easiest method is to arrive around 1 AM. Only one guard stands next to the maypole. Knock him out, climb up and take the maypole.
You can also arrange a date for a nearby girl or beat down her boyfriend as suggested by Prochek, the Tachov innkeeper, but this gives no reward and he is strong early in the game.
Return the maypole to Olbram in the morning and receive 45 Groschen and continue the quest.
Ruin the Laundry
Olbram next asks you to ruin Tachov's fresh laundry by driving sheep across it.
He gives you a laxative potion to poison the shepherd's food, but the simplest method is sneaking behind the boy and knocking him out. He is very weak.
Now herd the sheep through the laundry. Using a horse does not help much. A good method is shooting arrows behind the sheep to guide them.
This is a timed event. A sheep must run across the laundry four times to complete the objective.
A nearby innkeeper in red robes may complain, but the only consequence is a small reputation loss.
After finishing, scatter the sheep from the pasture into the forest. Olbram rewards 45 + 90 Groschen in total, if you complete the optional objective with laundry too.
If everything is done correctly, Olbram will offer the Battle of Frogs and Mice quest. Decline the fight, then talk to him again and choose the dialogue option about making peace.
Endings Setup
After finishing Frogs entirely, you now have 3 options:
- you can either go directly to the pasture (they will fight and you won't get an achievement)
- you can go to Troskowitz and investigate the pasture dispute with the bailiff (mandatory for the Truce achievement - read further)
- you can go do the Mice side quest, it will fail after you embark on the pasture for the fight. After finishing Mice and declining the offer to go directly fight on the pasture from Prochek, you can still investigate the pasture. This is recommended if you want the most of this quest.
Mice
The Mice quest is started with Prochek at the Tachov inn.
He may not offer the quest during some stages of Frogs. The safest method is finishing the sheep prank in Frogs, getting noticed, and agreeing to prank Zhelejov instead of fighting him. This starts Mice without failing Frogs.
On the way out, stop by Radovan the blacksmith to obtain the Lullaby Potion recipe.
Travel to Troskowitz and buy the paints from the merchant. They are expensive but there is no other way to obtain them. Killing the merchant immediately fails the quest.
Battle of Frogs and Mice (Truce)
Travel to Troskowitz and convince the Bailiff of Troskowitz to resolve the conflict.
You can pass Speech or Scholarship checks to access the record book. Scroll to the end near the window to find a Latin entry. Ask the scribe about it to learn about a border mark carved in a tree.
The pasture is west of Tachov. Find the tree in the center of the marked area and investigate the border sign.
Return to the bailiff and report your discovery. Then go back to the pasture with either Olbram or Prochek.
If Frogs or Mice are still unfinished at this point, those quests will fail and cannot be completed later.
After the confrontation begins, the bailiff arrives. Choose the first dialogue option asking him to stop the conflict. Henry then explains where the real border lies.
This resolves the dispute peacefully and unlocks the Truce achievement.
Rewards
After the resolution, speak to the bailiff again. He can give you the Master's Studies I Scholarship skill book, though it slightly lowers reputation.
The Battle of the Frogs and Mice questline ends here and the Truce achievement is complete. Congratulations.
Frogs & Mice FAQ
How do I get the Truce achievement in Kingdom Come: Deliverance 2?
Complete either Frogs or Mice first, then talk to the Troskowitz Bailiff and investigate the pasture dispute. Find the border mark carved in a tree west of Tachov, report to the bailiff, then go to the pasture with Olbram or Prochek. When the confrontation begins, choose the dialogue option asking the bailiff to stop the conflict. Henry explains where the real border lies and the Truce achievement unlocks.
Can I complete both Frogs and Mice before getting the Truce achievement?
Yes. The safest order is to complete Frogs first, then start Mice. If you get caught destroying the laundry in Tachov during Frogs, you can switch to Mice without punishment. After finishing Mice and declining the offer to fight from Prochek, you can still investigate the pasture with the bailiff for the Truce achievement.
Where do I start the Frogs and Mice quests?
Frogs is started by Old Olbram in Zhelejov. Mice is started by Prochek at the Tachov inn. Prochek may not offer Mice during some stages of Frogs - finish the sheep prank in Frogs first, get noticed, and agree to prank Zhelejov to start Mice without failing Frogs.
What happens if I report Olbram or Prochek to the other side?
Snitching will fail one of the quests and in most cases prevent the Truce achievement. Do every task quietly without killing anyone and never report either of them to the other village.
Where is the border mark tree for the Truce achievement?
The pasture is west of Tachov. Find the tree in the center of the marked area and investigate the border sign. You learn about it by passing Speech or Scholarship checks with the Troskowitz Bailiff to access the record book, then asking the scribe about the Latin entry near the window.