Ransom is a side quest in the 
Kuttenberg region available after the vast majority of other content in the area.
How to Start the Ransom Quest
First of all, note that this is a late-game side quest. Make sure you have completed the main quest The Devil's Pack (
The Devil's Pack) and side quests Bellatores (Bellatores) and The Spark (The Spark).
Many online guides claim this quest starts as a random ambush event on the road north of Danemark. We believe this is false.
We spent a lot of time fast traveling to Danemark from all possible angles, even got a few Cuman ambushes along the way. Zero of them were in any way connected to this quest.
Instead, we recommend you visit the inn west of Kuttenberg frequently and pester the local tipster innkeeper for information on new quests.
She will mention that a cart brought in an injured man last night and will mark the quest on your map (in the same inn). Before going there, make sure you have at least one Embrocation potion on you (sold by the Alchemist in Kuttenberg).
Go up the stairs and see Jan to begin the Ransom quest.
Heal Jan of Suchotlesky
Visit Jan of Suchotlesky in the inn west of Kuttenberg. Before the quest begins, you must treat Jan's injuries. This requires specific skill checks and items:
- Ankle: Medium Thievery check (to remove boot) and two medium Survival checks, requires a Bandage.
- Ribs: Medium Survival check, requires Embrocation.
- Fingers: Easy Thievery check, requires any Alcohol.
Make sure to fully exhaust dialogue in the inspection phase, before you move to the healing stage. After you've satisfied all healing requirements, Jan will explain his predicament and the Ransom quest will finally start.
Investigate in Sigismund's Camp
Jan asks you to negotiate for his brother Peter's release with a Hungarian nobleman Laszlo Farkas.
Head to Sigismund's camp northeast of 
Suchdol.
To locate Farkas, first ask any soldier for information. They don't know exactly, but will direct you to Father Bohumil (at the Field Chapel), Musa the Healer (at the Infirmary) and Milada (at the bathhouse).
To be most efficient, go directly to Milada and be prepared to pass the Very Hard Speech skill check to gain not only information about Farkas, but also Peter's whereabouts.
Find the Truth About Peter of Suchotlesky
Now go directly to Peter's supposed location in the prisoner tent, skipping the other objectives.
Peter of Suchotlesky location:
However the tent Peter is in is guarded by two soldiers. It is impossible to talk to them. Go to a building one above it and jump through the wooden fence to appear behind the soldiers, then sneak into the tent.
Sadly, inside the tent is not Peter of Suchotlesky but a random prisoner, Hynek of Hobza.
You need to either pass a Charisma check or bring him a piece of meat as bribe. He will then explain that Peter of Suchotlesky is, surprisingly, dead.
Once you are done with Hynek, sneak from the tent by hugging the right wall and crossing the bushes. This way the guards won't notice you on your way out.
Find Peter of Suchotlesky's Body
Hynek gave you not only information that Peter's dead, but also his body's location. Make your way to the southern end of the camp, near Milada's bathhouse.
Sneak through the carts until the path ends, then find Peter's body on one of the carts, like this:
Confront Laszlo Farkas
The next NPC you should talk to is Musa of Mali. He can not only pinpoint the location of Laszlo Farkas's tent, but also explain that Peter of Suchotlesky is dead due to negligence.
Run to Farkas's tent and talk to the guards. One of them will provide Farkas's description, after which you will finally get a precise objective location on the map.
Farkas's tent is here:
Locate Laszlo Farkas in his red tent within the Cuman section of the camp.
Laszlo Farkas looks like this:
You don't have to directly confront him with the truth. If you just play along, Farkas will show his true colours and will endlessly lie and will even try to up the price of the ransom. You can ask to see the prisoner, which he will deny.
After the first batch of dialogue, you can talk to him again and reveal that you know what happened to Peter of Suchotlesky. Farkas will not be happy, but will still insist on the ransom, even for a dead body.
Return to Jan at the inn west of Kuttenberg to plan the next step. He is now healed and walking downstairs.
Recruiting Reinforcements
Jan wants revenge for his brother's death. Depending on your progress in other side quests, you can recruit several groups of allies to aid in the upcoming fight:
- Devil's Den: Kubyenka and Adder. Speak to Kubyenka.
- Devil's Den: Mikesh and Kozliek. Speak to either of them.
- Thieving Guild: Stop at Hole in the Wall to recruit Hog and Goliath (complete The Spark).
- Menhard: Stop at Menhard's to recruit Arne who will help you (complete Ars Dimicatoria).
- Zimburg: Jan Posy and his brother (from Bellatores and Skeleton in the Closet).
Once you have enough help, return to Jan of Suchotlesky in the inn and set off for the meeting point.
Finale & Rewards
Agree to head to the meeting point with Jan. At the site, you must choose a side.
Side with Jan (Recommended): Suggest to kill Laszlo instead of taking the deal, like Jan mentioned earlier.
You must kill Laszlo and his 7 Cuman guards. If you did not bring allies, Jan is easily overwhelmed.
Reward: 125 Groschen and Peter's Sword (found upright in the cart). Do not loot the chest in the cart, or Jan will become hostile.
Side with Laszlo: You must kill Jan.
Reward: You can loot Jan's body (~500 Groschen) and take all of Peter's gear (Armor and Sword) from the chest in the cart without penalty.
This finishes the Ransom side quest in Kingdom Come: Deliverance 2.
Ransom FAQ
How do I start Ransom?
After The Devil's Pack, Bellatores, and The Spark, get the tip at the inn west of Kuttenberg. Bring Embrocation and heal Jan upstairs.
Is the Danemark ambush the start?
No. Use the inn tipster west of Kuttenberg, not a random road ambush.
Where is Peter?
Dead. Bribe Hynek in the prisoner tent, then find his body on a cart near Milada's bathhouse.
What is the best ending?
Side with Jan, kill Laszlo and 7 Cumans. Take Peter's Sword but do not loot the cart chest.
Who can I recruit?
Allies from Devil's Den, The Spark guild, Ars Dimicatoria, and Bellatores / Skeleton in the Closet.