Former motorcycle gang leader Kintaro Yajima is a widowed father dedicated to raising his young son, Ryuta. He leaves his delinquent past behind to work as a salaryman at Yamato Construction, a medium-sized firm where he performs cost calculations. Kintaro approaches office life with the same straightforward, fearless attitude he once applied to leading a gang, immediately clashing with the rigid hierarchy and corrupt practices of the corporate world.

The story is set primarily within the offices of Yamato Construction and the various construction sites and political backrooms of Tokyo. Kintaro finds himself caught between the company's honorable founder, Mr. Yamato, and the ambitious president, Oshima, who uses political connections to grow the company through underhanded means. After defending a hostess at a company party, Kintaro inadvertently insults a powerful politician, Tanioka, leading to lost contracts and his transfer to a remote branch in Tohoku. There, he works under Yozo Igo, a cynical, chain-smoking manager who spends his days drinking and playing mahjong while taking bribes from competitors.

Kintaro refuses to participate in the traditional practice of pre-arranging bids for public contracts, insisting on honest competition. His integrity impresses a local official, Handa, whose baby Kintaro rescues from a fire, leading to a direct confrontation with the corrupt system. When a rival company wins a contract through a fraudulent bid, Kintaro exposes the conspiracy, causing the shamed Handa to commit suicide. This draws the ire of the Tempoh Gang, local yakuza hired to silence him. Kintaro is kidnapped and beaten, but he is rescued by Igo, who reveals the deeper scheme by Tanioka and Oshima to drive larger construction firms out of business and form a monopolistic conglomerate.

As violence escalates with mail bombs injuring Kintaro's son and Igo, Kintaro decides to fight fire with fire. He calls together two thousand members of his old motorcycle gang, the Angels, to march on the city. When the police block their advance, Kintaro and his yakuza brother proceed alone to confront the Tempoh Gang, nearly killing their leader before Igo arrives to stop him. Kintaro is arrested, but his actions expose the widespread corruption. A young executive provides evidence of Tanioka's bribery to prosecutors, leading to a wave of arrests. Kintaro receives a suspended sentence and leaves the courthouse a hero, celebrated by his supporters and reunited with his son. The television series expands on this foundation, following Kintaro through multiple seasons as he navigates new corporate takeovers, yakuza entanglements, and his unwavering commitment to living honorably in a world of gray morality.