The Reactor | Main Quests - Tacarigua Risen 3 Guide

Way to unlock the quest: Talk to Erasmus (Taranis isle)

Quest giver: Erasmus

Horas has the last monolith stone on him

You can unlock this quest while on the Taranis isle, i.e. during the conversation with Erasmus that is staying at the mages HQ. Just to remind you, Erasmus asks your help at finding three Monolith Stones. To get the first one, you need to go to Tacarigua. The item is in possession of Horas, who is hiding to the West of the town of Puerto Sacarico (point 1b on the map). To learn more about this quest, see the walkthrough for the "A Follower of Magic" main quest.

Note - After you find Horas, you can return to Taranis with him. After you do, go back to the chapter with the walkthrough for the main quests on the isle.