This page in our guide to GreedFall contains a walkthrough for Promises Set in Stone, Siora's side quest.
Where to start the quest?: Complete Siora's previous mission and participate in The Trials of the Water main quest.
Go to Vedrad and talk to missionaries about the deal with Queen Bladnid. You have to find a stone engraved with inscriptions in Falrihistel. Go to the appointed place, pick up the stone and run to talk to Caradeg.
Search his workshop, which was obviously trashed. After subsequent conversations, you will finally find Caradeg. You need to convince him to cooperate. You can use Intuition talent or intimidate him (-1 reputation with Siora and -1 with Naut).
Go back to the village. You can speak with the missionaries before you talk with Eseld. You can accept their offer and gold - this will result in +1 reputation with Theleme. However, you will lose -1 reputation with Siora.
You can also tell Eseld about what you have learned. You will gain +2 reputation with the Naut and you lose -1 with Theleme.
The quest is complete - you get 1,300 XP and get + 3 reputation with Siora. You can continue the events in The Queen's Farewell side mission.