Oshichi, a famous girl detective, takes it upon herself to investigate the murder of a woman which occurs during an event for the festival of Asakusa Shrine. Her investigation leads her into danger as she runs afoul of a high ranking official and his plans to find a hidden treasure.

A princess finds life behind the protection of her brother and the high walls of the mansion to be quite dull, so she takes on another identity and lives in a small house in Edo pretending to be a singer but all the while she is actually a Shogunate Detective. Framed by a crooked magistrate for a crime she did not commit, Oshichi must clear her name of false charges after a woman helps to lead a prison break of the notorious Oshu Remnants. Meanwhile the magistrate, Lord Kai, conspires to be rid of her brother, Clan Elder, Lord Abe Iyo. Her only clue is an ornate dagger with a handle made of golden coins.

A mysterious coin found at a murder scene stirs the curiosity of young actress detective Oshichi and her brother Hyoma, who set out on a private investigation to unveil the secrets hidden behind the coin.

The death of a samurai in a palanquin leads girl detective Oshichi to take action to crush a plot to overthrow the Shogunate.