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Off the coast of China on Sulow Island, a haven for corruption and greed, in the Green Dragon gambling club, unemployed American merchant sailor McMillen bets the last of his money.  Beside him, a suave, sophisticated woman, Tamara, places her chips down and accidentally knocks McMillen's chips onto another number, which loses.  When McMillen protests and demands to see the club's owner, Hu Chang, he is thrown out of the club.  Hu Chang apologizes to Tamara and inquires after her uncle, Wong San, but Tamara replies indifferently.  She departs,and Hu Chang has his henchman Pedro follow her.

Tamara confuses Pedro with the help of her companion, Lotus, and meets Wong San in a warehouse belonging to her fiancé, Paul Lowell, an importer-exporter.  Wong intends to sell priceless jade pieces from the Ming Dynasty to purchase food and housing for the poor of his province in mainland China.  Lowell offers to purchase the pieces for a London dealer, which arouses Wong's suspicions.  When Powell offers $10,000 of his own money to secure the deal, Wong grudgingly agrees.  Lowell and Tamara plan to complete the deal the following day and later depart for Hong Kong.

Meanwhile, McMillen, broke, goes into an American bar, where Juan, the bartender, directs him to Frenchie, the captain of the Sally Ann .  Frenchie initially refuses to hire McMillen because of his reputation as a drinker, but changes his mind after witnessing a brawl in which McMillen prevails.  The next day Lowell meets Wong to authenticate the jade, but when he offers Wong a promissory note, Wong refuses to conclude the deal.  Lowell murders Wong and hastily arranges to transport the art pieces on the Sally Ann.  Hu Chang and Pedro arrive at Lowell's warehouse and after discovering Wong's body, learn from an informer that Lowell has departed on the Sally Ann.  Hu Chang notifies Tamara and chides her for not making arrangements with him.

Affronted by Lowell's cold-blooded callousness, Tamara sheds her European trappings and resumes her true Chinese identity and former profession as a pirate.  Hu Chang promises to provide her a boat and crew to track down the Sally Ann and regain the treasure.  Later, despite engine problems, Tamara's boat overtakes the Sally Ann and, with Pedro's assistance, secures the art and brings an unconscious Lowell on board her boat with McMillen, who replaces her dead engineer.  When Lowell revives, he attempts to explain his actions, but when he threatens Tamara, Lotus stabs him to death.

Back in port, Pedro knocks out McMillen, who later tells Juan about the day's events.  Juan realizes Hu Chang's involvement through Pedro's participation and reports them to the police.  Tamara and Hu Chang, meanwhile, discuss taking the treasure to Indochina, the only safe place to sell the pieces.  Tamara, suspicious of Hu Chang, refuses to carry Pedro on the voyage.  Later, McMillen follows Tamara and demands the money he would have won at the Green Dragon.  Instead, Tamara hires him for the voyage and admits she wants to sell the treasure to fulfill Wong's desire to help their people, but believes Hu Chang will interfere.

At the dock, Hu Chang insists on accompanying the shipment.  During the voyage, Lotus discovers a note revealing that Hu Chang intends to take over the boat.  Despite her efforts, Hu Chang succeeds, directing the boat to a small cove where Pedro and his henchmen await.  Pedro shoots Lotus, and as McMillen guns the engine to make a getaway, Hu Chang leaps overboard.  Tamara confides to McMillen that Lotus was her sister and mourns her death as the boat's engine stalls.  Knowing Hu Chang and Pedro will follow, Tamara and McMillen decide to resist, despite the odds.  In a heavy fog, Pedro and his men attack the boat, but McMillen and Tamara fight them off, although Tamara is stabbed.  McMillen then rigs the boat with explosives before getting Tamara to shore.  Hu Chang reaches their boat and detonates the explosives while searching for the treasure.  As Tamara dies in McMillen's arms, she reflects on how her only attempt to do good failed.