A fantastic journey of discovery into the world of literature. A letter with a mysterious message, a creepy woman who suddenly appears everywhere, and a puzzling book without an author create confusion for Nils and his cousin Berit. The two investigate, jot down their observations, and exchange thoughts through a diary: The woman's name is Bibbi Bokken, she receives countless books by mail that seemingly disappear without a trace, and she possesses a magical library filled with books that have yet to be written. New puzzles keep emerging, and the children increasingly feel like characters in an inscrutable game.