How about a survivor from some previous expedition that has insinuated himself into a position of power with some natives because he looks different? His difference in appearance makes the natives regard him as some sort of celestial, when in fact he was a cabin boy or other nobody from long ago. The appearance of others who look like him threaten his position, so he tries to do in the party, maybe by telling the natives they are "evil celestials" or something similar. If the party is good, they don't really want to go hacking up duped natives; the "celestial" survivor from the first expedition is important for clues to advance your major plot, but is generally uncooperative.