The world of Understockholm is one of magic and of lost things, of people who fell between the cracks and a broken mirror to the world of Överstockholm ("Stockholm Above"). The players created the market themselves, each group setting up a space and bringing something to trade, be it a lucky charm, a nice hat, a dream or a bowl of hot soup.
In play each group had one mission appointed by the organizers and a strict no violence policy called The market truce. Aside from these restrictions the players were free to explore the market, interact and create their own stories. The organizers played supporting roles as Spirits of the market. They were present as helping hands, performed rituals when a group succeeded with their
misson and gave out punishment when the market truce had been broken.
No characters or plotlines from the original novel were used, except the concept of the Floating Market.