Half a Confession introduces itself as a thriller and abruptly changes gears, transforming into a tale of morality with deeper insights into its characters than we had anticipated. It begins when Soichiro Kaji (Terao), a retired detective, walks into police headquarters and confesses to the murder of his wife. We learn that the victim had prematurely developed Alzheimer's after the tragic death of their son, and in her suffering, had asked to die. The police chiefs would be far more content to take him at his word if it were not for a conspicuous hole in his story: 48-hour gap between the alleged murder and his confession. Fearing a public relations nightmare, they are eager to bury the incident and keep the press in the dark.

A young samurai stuck at the bottom of the hierarchical order attempts to rescue his childhood sweetheart from an evil clan lord after learning of a plot to kill her and her infant child. Bunshiro Maki is a skilled swordfighter who's lethal with a blade, yet still can't rise through the ranks of the system. After his father is accused of plotting against his clan and forced to commit ritual suicide, his longtime love Fuku is sent to Edo to become the clan lord's concubine. A few years later, Fuku has bore the clan lord a son. When Maki learns that the clan has hatched a plan to kill Fuku and her son to secure succession to the throne, he recruits two childhood friends to help thwart the diabolical plot.