On April 3, 1478, in the castle of Cardona, Mauricio Coloma, receives from his father (unjustly sentenced to death) a confession that he descended from Jews, and that he will find hidden at his house a fabulous emerald ring, which passed from father to son, and will serve to Mauricio to start a new life in the Florence of the Medici. From the hand of Mauricicio, the reader will discover the Florence of Lorenzo the Magnificent, Leonardo da Vinci, and Pico della Mirandola. Mauricio also know Lorena, eldest daughter of a bourgeois family, whom he married despite opposition from her family and Luca, the candidate that was chosen by her family, creating enemies for life. In Florence, Luca will revenge of Mauricio, accusing him of betrayal the republic and making his incarceration. Once released, Mauricio will have to fulfill the promise made at the deathbed of Lorenzo, returning the ring to its rightful owner.