San Francisco, 1878. Ah Sahm, a newly arrived Chinese immigrant with serious fighting skills, is introduced to Chinatown's most ruthless tong, the Hop Wei, by Chao, a fixer. After impressing Young Jun, son of tong leader Father Jun, Ah Sahm is branded and taken to a brothel, where he befriends Ah Toy, a courtesan with connections.
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 hug scene in an alley next to an Irish bar, The Banshee. Penny Blake, the young wife of San Francisco's mayor, finds herself in a bind while visiting the wharf with her Chinese manservant, Jacob. Ah Sahm pays a steep price for playing the hero. The Long Zii clean up a mess, and brace for more bloodshed.
Leary pressures gentleman industrialist Byron Mercer, who is Penny's father, to hire his men for a cable-car track job?-?despite the fact that Mayor Blake hasn't yet awarded Mercer the contract. 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. Buckley urges Mai Ling to eschew restraint and start a war with the Hop Wei.
Big Bill finds himself compromised by his gambling excesses, but discovers a possible solution after an opium-den raid. Penny reveals the circumstances that prompted her to marry Mayor Blake, who's determined to show voters he won't tolerate San Francisco's "Yellow Peril". 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 through the Sierra Nevada, 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, looking for a lucrative payday.
Tensions escalate between the Hop Wei and Long Zii after an assassination attempt during a boisterous Chinatown parade. Big Bill sets out to pay his debt to Jack Damon, leaving Lee to keep watch over Lucy and the kids. 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 unsavory choice in order to save her home. Lee's past catches up with him.
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, while Penny struggles to hold her tongue. Mai Ling warns her brother against waging a battle he may not win.
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. Ah Sahm remembers his roots as a fighter, as Ah Toy warns him of the dangers that await. 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 honor her partnership.