You ask each other questions to figure out who the spy is while the spy tries to figure out the current location. You have to ask questions that are vague enough to not give away the location but specific enough to prove you belong there. The tension for the spy is incredibly high as they desperately try to blend in. It requires quick thinking and a lot of bluffing. It takes literally two minutes to explain the rules. You can play it anywhere since it requires almost zero table space.