13 Assassins is a movie that takes place during the eighteen-forties. Japan was going through a time of peace. This was during the final years of the samurai. Lord Matsudaira Naritsugu is the younger brother of the current Shogun. He is a very evil man in nature. Matsudaira likes to do whatever he pleases without any care as to it effects other people around him. Sir Doi Toshitsura is a government official. He is both concerned and aware of an increasing danger. He feels that this danger is approaching quickly and will do whatever it takes to keep Naritsugu form ascending to another rank in the governmental system. Sir Doi quickly hires an assassin to kill Naritsugu to prevent the impending danger although Naritsugu's guards learn of the hire. The assassin hires eleven more samurai who both himself and Sir Doi can trust. The twelve plan to attack their target on the long journey from Edo to his home.
To form a road block, a few of the samurai are sent ahead to bribe at town to close the road. This will force their target to go a different route that will lead him to a remote village. The others ride to the chosen remote village to set up for their ambush. Naritsugu has hired thugs to slow down the assassins while he is on his way in hope that he will have a safe journey. The band of assassins gets lost on the mountain trails. A fellow assassin who is familiar with the mountain trails, finds them and helps them off the mountain.
When they awake the next morning, they are made aware that their target has brought around two hundred men with him. They decide that they will continue with their plan even though they are outnumbered. The battle ensues and they trap their target in the village.