This quest will appear in your journal when you check the "Horn Thief" poster on the notice board during the "Where Misery Gathers" quest.
A rancher says bandits have cut off the precious horns of his goats. Listen to his story.
Rewards: 1.30 Silver, Medium Bag x1, Cloth Piece x5

1. Speak with the enraged man
Go to the location marked on your map, located at the Capra Pasture farm. There, you will find the author of the poster - a very angry man named Ibano. Speak with him to find out what happened.

2. Read the memory on the mysterious horn thief
Go to the new location marked on your map, this time situated slightly to the east. There, you will find a stash of stolen goods and three bandits who will attack you on sight. Eliminate them.

Use the lamp to reveal the bluish-white spirits and, after a moment, learn the "Hornless Goats" memory.

The memory should play automatically, however, if it doesn't, use the Visone helmet and start the memory manually by selecting it from the list.

Watch the memory until the end to complete this objective and receive the next one.

3. Find the stolen item
Pick up the Mysterious Elixir lying on the large rock, right next to the crates.

4. Return to Ibano
Return to Ibano - he has moved to Muckroot Ranch in the meantime - and hand him the elixir you found. This will complete the quest.

The hot-tempered rancher was reeling from a break-in of his own, but the thieves weren't after his coin, they wanted some piece of stone. Someone is clearly using these bandits as pawns to help secretly seek something out.