Grandpa and Sir Mano's favourite game, since their childhood, is the Nine Men's Morris. Zete and Rika get to know the game's rules, and they also learn about Europe's history, retrospecting nearly 500 years during the game. The story is built around the bells, emphasizing their importance from The Siege of Belgrade, in 1456, until the First World War. Grandpa and Sir Mano teach the kids how and why people used bells throughout history during the game.