A kind-hearted provincial governor, Taira Masauji (Masao Shimizu), has been exiled by his political opponents for his kindness and honesty to peasants, and before he departs tells his son to always remember “Without mercy, a man is not a human being” and gives him an amulet of the goddess of mercy. On the journey to visit Taira six years later in his remote island, his wife, Tamaki (Kinuyo Tanaka), and two small children are separated through the deceit of a priestess (Kikue Mori) they met in the woods. Tamaki is taken to a brothel on Sado Island while the children, Zushio (Yoshiaki Hanayagi) and Anju (Kyoko Kagawa), are forced to be slaves for 10 years to the ruthless and corrupt tax collector Sancho (Eitaro Shindo). Zushio has forgotten his father’s words of wisdom and cruelly punishes other slaves that Sansho’s own son, Taro (Akitake Kono), can’t because he’s too much of a weakling (Taro realizes his fate and becomes a monk). Zushio, now an adult, finally escapes and his sister drowns herself rather than to be tortured into informing on her brother. Zushio makes his way to the capital, Kyoto, where he learns that his deceased father is honored for his humanity, and he’s appointed governor of the province where Sancho resides in his fortress. Zushio frees the slaves and then resigns his post to search for his mother. In the end, after twenty years of misery, Zushio finds her, lame and blind, living in poverty in a hut on a distant island. Though there’s no resolution or comeuppance to the villains, the hard-pressed family is reunited spiritually.