In late Edo period of Japan, a vassal of the Akashi Domain named Tosho Mamiya (Masaaki Uchino ) commits suicide in front of the gate of Roju, the family of Lord Doi (Mikijiro Hira). By his suicide, he accuses the lord of Akashi Domain, Naritsugu Matsudaira (Goro Inagaki), with committing atrocities like murder & rape. Naritsugu Matsudaira, who is the younger brother of the shogun Ieyoshi, is set to become the Roju next year. The Shogun clan becomes disturbed by the case and believes the country's stability & peace is threatened by Naritsugu Matsudaira. Lord Doi then decides to assassinate Naritsugu Matsudaira and orders samurai Shinzaemon Shimada (Koji Yakusho) to carry out the deed.Shinzaemon Shimada gathers eleven men, including a butcher ronin named Kuzuro Hirayama (Tsuyoshi Ihara) & Shinzaemon Shimada's own nephew Shinrokuro Shimada (Takayuki Yamada), who is a gambler, alcoholic and womanizer. As their plan progresses, Naritsugu Matsudaira's head samurai Hanbei Onigashira (Masachika Ichimura) hears of the assassinaton plan. Years ago, Hanbei Onigashira & Shinzaemon Shimada were fellow pupils of the sword, but ideological differences led them to part ways. Now, a mental battle between Hanbei Onigashira & Shinzaemon Shimada begins.Shinzaemon Shimada believes the only way to assassinate Naritsugu Matsudaira is to ambush him in the town of Ochlai, while he is returning home from Edo. The assassins are dispatched to Ochlai to fortify the town and lay traps. During this time the assasins pick up a 13th member, a mountain man named Koyata Saga (Yusuke Iseya).When the 13 assassins' plan is set to begin, they encounter many surprises, none of which is bigger than facing an army of more than 200 samurais ...