This is one of the court quests you should complete to lure Ambrus out. This quest can be started by approaching the soldiers guarding a few barrels.
Ambrus's soldiers are busy transporting barrels of blood. I could make sure they don't reach their destination.

1. Defeat the guards
I've got to kill the soldiers guarding Ambrus's blood barrels.
Simply kill all the soldiers guarding the barrels.

2. Check the barrels (3 Time Segments)
Time to make sure these barrels never get into Ambrus's hands.
Approach the barrels and destroy them.

It will turn out that a man named Klaus the Brave is hiding in one of them, wanting to join the rebellion. You will be able to encourage or discourage him by choosing one of the dialogue options.
- You better drop this act while you still can.
- Keep on fighting, then. Crake will notice, eventually.
Reward: 250XP, Skill Point, Kobold's Blood x1.
3. Endings
If you told him "Keep on fighting, then. Crake will notice, eventually."
When I got to destroying the blood barrels, I certainly didn't expect to find a man hiding inside one of them. He wanted to join the manumits, and I encouraged him to pursue this goal. We need men like him.
If you told him "You better drop this act while you still can."
When I got to destroying the blood barrels, I certainly didn't expect to find a man hiding inside one of them. He wanted to join the manumits and I tried to talk him out of it - we don't need more people throwing their lives away like that.

Such an ending is possible during the night if you give in to the hunger.
When I got to destroying the blood barrels, I certainly didn't expect to find a man hiding inside one of them. He wanted to join the manumits - a dream he will never fulfil because I killed him.