Ninjas hired by Doi remove Hidetada's heart to test for poison, but lose it to a group including Akane, daughter of Yagyu, Iemitsu's fencing instructor.

Yagyu determines Hidetada was poisoned and confronts Kasuga and Matsudaira who admit to the crime, telling the innocent Iemitsu it was necessary to ensure his succession.

Hayate and Mon become Negoro fighters seeking to recover their Yamato Province lands, lost twenty years earlier.

Their leader, Sagenta, agrees to Yagyu's appeal for help, sensing an opportunity; Jubei arrives as they kill Doi's Koga ninja spies.

Iemitsu makes Matsudaira Chief Chamberlain and Yagyu Inspector General and prepares to fight his brother.

Doi secures Lord Date's support for Tadanaga and recruits fighter Ogasawara Genshinsai who offers help in exchange for becoming fencing instructor and vows to kill Yagyu.

Genshinsai persuades his old swordfighting apprentice Yukinojo, who performs kabuki, to dress as a handmaiden and attack Iemitsu.

The Negoro provide guns to the ronin supporting Tadanaga to attack Iemitsu en route, but they are slaughtered by concealed riflemen.

Okuni visits Lord Owari at Nagoya Castle to dance, accompanied by the blinded Sanza, who denounces Yagyu's trick attack.

The film received five Japan Academy Prize nominations, including best actor (Kinnosuke Yorozuya), best art direction (Norimichi Ikawa), best film, best screenplay (Kinji Fukasaku, Tatsuo Nogami, Hirō Matsuda), and best supporting actor (Shinichi Chiba).

[4] The film was adapted into a teleplay called The Yagyu Conspiracy which was broadcast by Kansai Telecasting Corporation for 39 one-hour TV episodes from 1978 to 1979.

A second TV movie remake starring Kōtarō Yoshida as Munenori and Junpei Mizobata as Jūbei aired on NHK BS Premium on April 11, 2020.