Ah, let me try to remember the whole thing, and not get my versions mixed up.
The most popular version (I think) is about a soldier who comes to a town and sees that the people are eating poorly. So he gets everyone together with a huge pot, and tells everyone to gather up at least one thing that they had from back home, and put it in the pot to make soup. So everyone manages to scrape up something, whether it be lamb, beet, carrot, steak, pepper, or something entirely different. However, one person has none but a stone, and puts that into the pot. Hence the name of the story, 'Stone Soup.'