"So what is this?" - pokes Mr. Nikétasz, former court orator, chief judge of the Byzantine Empire, imperial logothete, at the hard-to-read document pushed in front of his nose - Baudolino's adolescent diary, written in a language he created himself - around the beginning of the year of the Lord 1204.
And Baudolino begins to tell a story. Byzantium is being plundered by crusaders, Niketas' life is saved from them by Baudolino, the city is on fire, they have to flee, but Baudolino keeps telling stories. The hero of the picaresque copy novel that unfolds following his tale - the world-famous writer-philosopher's fourth novel - is himself, Baudolino, the adopted son of Frigyes Rőtszakallú of peasant origin. Moreover, his hero is extremely active: Baudolino's power of imagination and action knows no bounds. His main idea directly tries to steer the fate of the German-Roman Empire as a whole into a new path... However, the relationship between idea and reality - as is familiar from the highly successful Eco-novels - is very tangled.

Is "John the priest" from the Far East an actual person and did he write a letter to Barbarossa (the Pope, the ruler of Byzantium)? What do the biblical Three Kings have to do with the Grail legend, Charlemagne and the German-Roman Empire?

In any case, Baudolino and his friends decide to go to the end of the world themselves, to the country of priest János. And after an aborted crusade and the suspicious death of Frederick, only the good part begins: a years-long wandering reminiscent of the travels of St. Brendan and the adventures of Marco Polo... In the end (but even more so) everything comes to light again, of course.