An abnormally virtuous roper lives in a cavern where plentiful Rothe are to be found munching on a magical stone eating fungus. He has lived a generally peaceable and solitary existance and has no desire to do more than play the predator in his corner of the eco-system. However, recently a nearby tribe of goblins and a nearby tribe of gnomes have begun to war with each other over the caverns resources, raiding the others herds and slaying the herdsman, fouling each others drinking water, and destroying the outlying communities of the other. The roper is worried that if one side or the other gains the upper hand, they will surely expand into his territory once the threat of the neighboring community is elimenated. This will surely eventually bring him into conflict with the victor. Moreover, if he doesn't intervene, then many innocents on one side or the other will surely die cruelly. But from his distant vantage point, he does not know which side of the struggle is truly in the wrong. He is very hesitant to choose to intervene on behalf of the gnomes, since he believes that chiefly he would be judging things by thier appearances, and he knows to well how others would judge him by his appearance.
The PC's desire access to a deeper layer of the cavern complex, but the only known tunnel is through the roper's lair. The roper will only allow the PC's to pass in peace if they solve his moral quandry, thereby proving themselves to have good intentions and wisdom. (Alternately, a sense motive DC 35 will reveal that the roper is bluffing, and would actually allow the PC's to pass without harm if they insist to the point of violence, since he has no real desire to shed blood over so trivial of a reason.)