Described in her youth as very sane, why did things go awry in Juana's existence? Was her husband so beautiful? Did Juana suffer from a latent illness that accelerated with her distance from Castile? Did pregnancies accentuate a hitherto silent ailment? Did jealousy constitute the cause of her pathology? Why was Isabella the Catholic allowed to reign at the end of the Middle Ages and not her heir, in the middle of the Renaissance, with humanism as doctrine? Did Juana use the alienation she was accused of as a neural mask? What values did she cling to in order to maintain her courage in the face of her captors? For almost 50 years Juana, Spain's most famous and yet least powerful queen, was confined to the palace of Tordesillas. She was 29 years old when she arrived and died in that enclosure at the age of 75. Except for childish laughter, throughout her life she was treated like a puppet. She, who was the wisest princess of her time... Without looking for it, Juana was on the board a pawn moved at the whim of her father, Ferdinand, her husband, Philip, and her son, Charles. It is said that behind the history of chess, brought to the Iberian Peninsula by the Muslims, there is enigmatically hidden the figure of her mother, the Lady... Isabel designated Juana as heiress in her will, although in practice her mandate was ignored. With patience and scientific rigor María Lara, PhD in Modern History, reconstructs the daily life of Juana de Trastámara, from the investigation of her birthplace to her death on Good Friday after being branded a heretic. Researching in the archives, the writer delves into the emotional universe of Juana, the empress whose title was never recognized, the mystic who lived with Philip's corpse as the key to her freedom. This is the story of Juana, the sane queen.