Warning: Wikipedia contains spoilers
Jernau Morat Gurgeh, a master gamesplayer from the Culture, is bored with life. The Culture's Contact section suggests that he goes to participate in a games tournament in a savage alien empire, the Empire of Azad, where a complex game is used to determine social rank and political status. He belatedly discovers that his participation is essentially a Culture takeover plot, and that he, the player, was in fact a pawn in a larger game.