So exploring to the black isles leads to a strange encounter with a group resting there. This encounter can either solved peacefully or in combat. But one of your crew is there. Last time I did that encounter it was Handsome Eliam. Peacefully resolved led to them breaking up camp and leaving you alone. Handsome Eliam was gone from my crew after the encounter.

According to wiki:

 

If you try to inspect the hooded man, you may find a hairless head with no eyes, or you may find that it is has killed one of your crew members and taken their form. Either way, you will suddenly appear back on the world map, with the camp nowhere to be seen.