A series of grotesque murder cases takes place on rainy days. Detective Hisashi Sawamura (Shun Oguri) works to catch the murderer like he has done with past cases, but he soon realizes the murderer's next target is his wife and son. A man in a frog mask is a suspect.

In a poor district of Edo lives a young samurai named Soza. He has been sent by his clan to avenge the death of his father. He isn't an accomplished swordsman however, and he prefers sharing the life of the residents, teaching the kids how to write etc. When he finally finds the man he is looking for, he will have to decide whether he follows the way of the samurai or chooses peace and reconciliation.