Holy Spider follows the terrifying true story of one of the most feared serial killers in Iran who operated between the years 2000 and 2001. Saee Hanaei, known as “Spider Killer” embarks on a “spiritual” journey where he is convinced he has to clean up the Iranian city, Mashhad, of the corruption and immorality that, according to him, the city’s prostitutes do to “dirty” the city. After killing 16 female sex workers, he grows increasingly desperate with the city’s public’s lack of interest in his “divine mission”. It is then that journalist Arezoo Rahimi goes to the city to investigate the murders.