Mila, Felix and Julian are spending the summer with their grandmother and Mila's friend Emilia. Since their plans have been thwarted by bad weather, they decide to go rummaging in the attic, where Mila finds an old, dusty game board with old cards that have nothing written on them. But when they start the first round, writing suddenly appears on the back of the cards... When the children open their eyes again, their familiar surroundings have vanished and they find themselves in the Middle Ages, of all times! Sigurd the Terrible rules here, instilling fear in his subjects. Not even the princess can stand up to him. What can four children possibly do? If it weren't for the children's special gift for solving puzzles and making plans...