Green stones that shine in the darkness: these are the contents of a secret compartment in the amulet found by Aquila della Notte. Their appearance is harmless but, as El Morisco explains, they cause sudden mummification. The mineral is used as an instrument of death by the followers of Tulac, an Indio army leader known to Eusebio, the servant of the scholar from Pilares. Tulac wants to give Mexico back to the descendants of the Aztecs: he is the head of the gun-running trafficking, organized by El Dorado and by his desperados. In order to trap the bandits, Tex and Kit Carson ally themselves with the Rurales.