So we're on our way to fight the final boss of the campaign, who is a former ally that's been possessed by an evil entity. This thing can only be expunged by beating the possessed until they're almost dead, and then the only way to hurt the thing itself is with a special weapon it has on its person so it can't be used against it. It's very important that we don't let the BBEG know we know what's going on, so they won't try to run away or something and we can steal the one weapon we need to save the world. During the lead up as we approach the battle, our druid blatantly asks the final boss about the plans of the possessing entity, throwing any chance of being able to steal the weapon while its guard is down out the window, and nearly ruining everything forever.