Interesting - a switched-at-birth story based in France during the reign of King Philip IV and his sons.
The first five chapters of the book deal with the story of Giannino di Guccio who is told that he is the real King of France, though switched at birth, by Colia di Rienzo, Senator (sometime Dictator) of Rome. We follow Giannino as he leaves his home in Siena to set out to prove (by what ever means) that he is indeed Jean I, King of France.
France at this period was locked in a bitter struggle with England over who was entitled to inherit the French throne after the death of Phillip the Fair and his sons. It it the time of the Hundred Years War - and there are many factions eager to see a destablising of political power in France.
The second half of the book deals with the author Tommaso di Carpegna Falconieri's search for the truth behind the story. Was Giannino myth or real? Was his story real or a complete fabrication? Was there any historical "truths" that could support or not such a story.
Falconieri was not the first author to write of Giannino - those who have read Maurice Druon's "Les Rois Maudits" would be familiar with his story.
So fact or fiction - I'll let you decide.