Raizô Ichikawa is a ronin and happy to be one. He wanders around town righting wrongs. Women try to seduce him. Lords try to hire him, but he doesn't care. Only Shunji Sakai attaches himself to him. But it turns out that Ichikawa is the twin of the heir to a principallity, also played by Ichikawa -- the heir, not the principality -- who was exiled so he would not threaten an orderly succession. Now there is a conspiracy against him, and his twin wants to help.
It's one of the Daei samurai flicks, which means decent production values, some good acting by Ichikawa, and a story that borrows heavily from both the legends of Momotaro -- Ichikawa's ronin is called Momotaro, and Sakai's character is literally called 'Monkey' -- and The Man In The Iron Mask, confident that its Japanese audience will sort it all out in their own minds. For westerners like me, it seems best to ignore the linkages to the Japanese movie and enjoy it as another silly little samurai flick, full of high standards, weird behavior, and general betrayal.