Alan Gaskell (Clark Gable) is an abrasive, gambling, captain of a tramp steamer, the “Kin Lung,” chugging between Singapore and Hong Kong. Tensions are high before the Kin Lung sails from Hong Kong because pirates are discovered disguised as women passengers while others try to smuggle weapons aboard.
Dolly Portland (Jean Harlow) is Alan’s former girlfriend, who Alan later describes at the Captain’s table as a “professional entertainer,” and travels with her maid. Meanwhile, another of Alan’s former loves, aristocratic Sybil Barclay (Rosalind Russell) from Sussex, England boards the Kin Lung. “I am in your hands again,” Sybil taunts Alan, and eventually they plan to marry when the steamer docks in Singapore. However, Dolly tries to win back Alan. Meanwhile, Jamesy McArdle (Wallace Beery) is a corrupt passenger, in league with a gang of pirates planning to steal the gold shipment of GBP250,000 gold bullion carried on the steamer. Dolly discovers the plot and attempts to warn Capt. Gaskell against McArdle but he deflects her warnings.
In calm seas, following a typhoon in which the ship suffered damage to its cargo and the deaths of some crew, the Kin Lung is boarded by Malay pirates, as McArdle expected and with whom he is in alliance. The pirates steal personal possessions from passengers. Unable to find gold in the ships strongbox, which Capt. Gaskell has replaced with sand, they torture Capt. Gaskell using a Malay Boot but the captain will not reveal the gold’s location. Instead, with bravado, Gaskell instructs the pirates, as they prepare to torture him: “My size is 9C”, before fainting from pain. While leaving the ship, minus the gold they intended to steal, the pirate’s ship is bombed by 3rd officer Davis, who dies while throwing a Mills Bomb as a grenade, and later strafed by Capt. Gaskell. Their ship sinks in the China Seas.
Frustrated by the failed robbery McArdle commits suicide. When the Kin Lung docks in Singapore, Captain Gaskell, still limping due to his torture, settles that his love for Sybil is superficial. Instead he recognises that Dolly gave him good warning and he loves her more. They decide to marry. He says farewell to Sybil. As the film closes Capt. Gaskell reveals the gold was safe all along, hidden inside the ship’s cargo (the toolbox of a steamroller stowed on deck).