The Ivory Horn is an off-screen companion adventure in Pillars of Eternity.
In-game description
The pitch:
Explorers in Eir Glanfath discovered an ivory horn of disputed provenance. Many Glanfathans believe it was stolen from an Engwithan ruins, but the explorers claim it was dropped by an early dwarven expedition.
The explorers were waiting for Dyrwoodan arbitration in Eina's Rest when thieves attacked the group, killed several members, and stole the horn. Its current whereabouts are suspected to be somewhere along the Isce Îen River.
The conclusion:
[Companion Name] tracked the ivory horn's thieves all the way to Forked Vale. After a small skirmish, two thieves were dead. Rather than die for the horn, the remaining thief dropped it and fled. [Companion Name] recovered it and returned it to the arbitrators in Eina's Rest. After a ruling in their favor, the remnants of the expedition gave [Companion Name] the Nautilus of Or-Grammon, a wondrous enchanted shell from the Deadfire Archipelago.