While in exile in Costa Verde, XIII and his father, Mullway, attempt to find a treasure hidden by their ancestors somewhere in Mexico. Giordino, meanwhile, fabricates evidence claiming that XIII is Seamus O'Neill, an IRA operative who trained under Fidel Castro. As O'Neill, XIII is wanted by the US government, but he again manages to escape. He also survives an assassination attempt by Irina Svetlanova, who has taken over the Mongoose's operation. After many setbacks, the treasure is found and then lost again. Meanwhile, Giordino is removed from duty by the new President, who has received evidence from XIII and Mullway revealing that Giordino is not only connected to the Mafia but also that he killed Walter Sheridan.