When the antique dealer and ancient books seller Artur Aiguader is found dead in his shop in Barcelona, his step-son and writer Enrique Alonso flies to the city to take charge of Artur’s things.

Only a few days before the crime, as if it were an omen, Artur wrote a letter to Enrique telling that if something happened to him, Enrique should look for a manuscript hidden among the volumes in his library, a text from the 15th century written in Latin and yet to be translated. The manuscript seems to have been written by Casadevall, one of the architects of the Cathedral of Barcelona.

Now, Artur has been killed and Enrique, aware that the police should be allowed to do their job, is the only one who knows about the connexion between this death and the old manuscript. He can’t help trying to find his father’s murderer on his own, while at the same time uncover the secrets that the Casadevall manuscript seems to hide.

The investigation reveals that Artur wasn’t only a good, educated and caring father, but also someone who acted as an intermediary between rich collectors of antique art and art traffickers. Besides, the translation of the manuscript offers him a journey to a past time in which Christians, Jews and scholars of the Kabbalah were trying to find ‘The Stone of God’: a big emerald on which the true name of God would be engraved…