Check the chieftain dwelling

Using your invisibility you enter the village, and you manage to reach the chieftain's dwelling easily.
There is a long corridor, and he's drinking alone, posing his feet on a female human slave who has piercings on her nipples and genitals. She eats food rests from a pet bowl. The goblin laughs and plays with his golden crown and his white beard.

He didn't notice you, you can try to assassinate him, or you can prepare to fight and defy him.

If you assassinate the chieftain, you can search the dwelling for useful items to complete your quest.
If you defy him, you can earn the respect of the tribe, and you can force them to reveal the location of the stone or help you.