Lieutenant Pereira is puzzled by the mysterious murder of a prostitute: it's the second time a woman has been found with her nose cut off, and a special plant known as a "goosefoot" placed beneath her corpse. Suspecting that the killer is basing his actions on the medieval board game of the Oca Brothers, Pereira asks Professor Rinaldi for help. His insight comes too late however: Tea, a young girl on a pilgrimage with a group of young offenders and their minder Leyva, is found murdered.

El esoterismo y los ritos medievales son la base de una serie de crímenes sangrientos que investiga la policía. La situación se agrava cuando el robo de un importante cuadro coincide con el crimen ritual de una prostituta. El juego de la oca, un entretenimiento muy practicado por los peregrinos a lo largo del Camino, encierra la clave para resolver el misterio. La partida ha comenzado y nuestros personajes van a jugar.