In 1782 winter, Maria Luisa of Parma princess is expecting a child from one of her lovers as an inevitable consequence of her countless extramarital affairs. In a passion outburst, she writes to the baby´s father to tell him the news. In that letter, she recognises the illegitimacy of the child she is carrying in her womb, who some years later would be known as CarlosV, the pretender. With this beginning, the novel turns into an exciting historical thriller. The letter ownership becomes the core of the plot, causing deaths, conspiracies, the Inquisition incursions and even wars. The document is so important that the Jesuits, the colonel Zumalakarregi at that time, Sabino Arana, Arturo Campión and; finally, the Basque government will look for it for two hundred years. It is a fiction novel based on real facts.