From the introduction: Contagion is a role-playing game in which a group of players (typically 2-6, but conceivably more) get together to tell a story set in the world of Contagion. Using the rules in this book, each player creates a unique character, whose actions they will control through narration, role-play and dice rolling. One player, called the Gamemaster, will adjudicate the rules, create, describe and control the setting elements such as locations, items and non-player characters, and assist the players in crafting a story.