One night, a mysterious visitor stumbled upon the village of *insert name here*. He was very sick, and asked for a place to stay the night. One by one, doors were slammed in his face. But when he came upon an inn, the owner had pity for him and let him in. Turns out that the illness is contagious, and within days, the whole village is infected. The King (for this was in the time of castles and knights), who had feasts at his palace every night, and could not possibly need for anything (as his castle was filled with gold and riches), ignored their requests for help, and continued throwing his fancy feasts and balls. By now the villagers were desperate for a cure. And so when another group of travelers came upon the village, they promised them food and a place to stay, for three moons, all free of charge, in exchange for finding the cure and bringing back enough for the whole village. Of course, they accept, for who can resist the sound of free food and shelter when they are so weary and tired from their travels? But at dawn, they realize that finding the cure, and bringing back an amount large enough for the whole village, is harder than it sounds. But they've already accepted, had supper, and spent the night, so how could they possibly go back on their word? So by noon they are restocked on supplies, and are sent on their way to who-knows- where.
You are one of the travelers, and need to find the cure, bring it back, and give it to the villagers before any of them die.
I think the cure should probably be an herb of some sort, and the travelers could find a fortune-teller to tell them what it is and where to find it.
Of course, it's going to be a hard and difficult journey...