An ex-Marine haunted by a tragic past returns to his hometown of Pittsburgh and enlists his father, a recovered alcoholic, and his former coach to train him for a mixed martial arts tournament.

San Francisco, 1878: Ah Sahm, a newly arrived Chinese immigrant with serious fighting skills, is introduced by a fixer named Chao to Chinatown's most ruthless tong, the Hop Wei. After impressing Young Jun, son of tong leader Father Jun, Ah Sahm is branded.

Intercepting a shipment of opium at the docks, Young Jun, with Ah Sahm and his Hop Wei lieutenant Bolo in tow, decides to send a message to Long Zii. Big Bill and Lee investigate a grisly murder scene in an alley, and Ah Sahm pays a steep price for playing the hero.

Leary pressures Byron Mercer, Penny's father and a gentleman industrialist, to hire his men for a cable-car track job. Accused of assault and perhaps worse, Ah Sahm gets a cold shoulder from the Hop Wei, with his fate in the hands of an unexpected ally.

Big Bill finds himself compromised by his gambling excesses, but discovers a possible solution after an opium den raid. After meeting with leaders of the Fung Hai tong, Mai Ling offers Ah Sahm a way out of a protracted - and bloody - tong war.

Transporting precious cargo via stagecoach, Ah Sahm and Young Jun are forced to spend the night with three strangers at a frontier saloon in the middle of nowhere. The detour turns perilous when Harlan French, a notorious outlaw, shows up with his henchmen.

Tensions soar between the Hop Wei and Long Zii after an assassination attempt during a boisterous parade. Big Bill sets out to pay his debt to Jack Damon. Mayor Blake and Deputy Mayor Buckley get a mandate from Robert Crestwood, a senator with eyes on the White House.

Ah Sahm faces a dilemma when Father Jun sends Bolo to hunt down Long Zii and Mai Ling. Ah Toy recruits a special girl from a whore monger, and takes on a business partner for a land deal. Penny is faced with an unsavoury choice in order to save her home.

The Hop Wei and Long Zii consider a novel way to end hostilities. Ah Toy and her real-estate business partner hit a bump in the road in their effort to buy a valuable piece of land. After promising jobs to Leary's Irish workers, Mercer toasts Crestwood at a fundraiser.

Chinatown gathers to witness a prize fight between elite warriors from the Hop Wei and Long Zii. Buckley plays a bluff in hopes of getting Mercer to lower his fee. Bill and Lee question Wang Chao about the recent series of sword killings in San Francisco.

Ah Sahm rejects his warrior roots and retreats into the netherworld of the Chinese working class. A guilty Big Bill stands vigil for Lee at the hospital. Zing and the Fung Hai make a show of force to compel Mai Ling to honour her partnership.

Back with the Hop Wei, Ah Sahm spends his nights at the Barbary Coast fight pit, confronting a new anti-Chinese group: Teddy's Boys. While Ah Toy accuses him of just looking for another fight, an empowered Mai Ling worries about her brother's next steps.

Ah Sahm and Young Jun search for a discreet place to hide their product after striking a deal with a new opium supplier. Mai Ling sends Li Yong and Zing to deliver a message to a rival tong. Penny asks for Ah Sahm's help in protecting her factory.

With their new enterprise going well, Young Jun shares his worries with Ah Sahm about the new men Father Jun has brought over from China. Meanwhile, Chao goes to Mai Ling for help keeping Zing away from his business, and things take a deadly turn at Bill's home.

As the police prepare for retribution, Chao comes to Bill with a mutually beneficial offer. A sympathetic Sophie offers Leary a new plan. Ah Sahm and Penny have a moment when he confides his plans for the future. Buckley urges Blake to take a stand against the Chinese.

A guilty Mai Ling tries to make things right with Ah Sahm. Penny finds her business in trouble and learns that Ah Sahm has been using her. Ah Toy pays an emotional visit to Nellie's Sonoma winery. Bill and Chao put their plot against the Fung Hai into action.

Ah Sahm, Young Jun and Hong travel with Vega to U.S.-Mexico border town Rooker's Mill, owned by Elijah Rooker, for a fight tournament with a hefty cash prize. As he learns more about Vega, Ah Sahm draws the attention of another fighter, Dolph, and later, Rooker himself.

Jun face off. Ah Toy takes matters at a sadistic rival brothel into her own hands. Leary is urged to utilise his political influence. Just as his heroics are praised, Bill is faced with another murder.

The police shut down Chinatown in their hunt for a killer, just as the Hop Wei make a move that puts Mai Ling on edge. Buckley steps into a new role and considers a proposition from Leary, who faces questions from the Irish workingmen. Ah Toy fights for her life.

After Bill and his men are confronted by an angry mob, Chinatown erupts into chaos, forcing the tongs to work together. As Chao and Mai Ling seek shelter, Mai Ling tends to an ailing Ah Toy. Sophie opens her eyes to Leary's world; Lee decides which side he's on.

Young Jun faces a crucial decision after Mai Ling tries to drive a wedge between him and Ah Sahm, who takes the opportunity to go on the offensive against Leary. Resolved to take Buckley down, Penny goes to the press. Mai Ling finally plays her hand against the Hop Wei.