Steve Costigan, a robust and formidable sailor, is set to fight Slip Harper in Shanghai's Amusement Palace Fight Club. Instantly, Steve takes a dislike to the fight's referee, Red Hoolihan, a large, swaggering man. The dislike is mutual, and tensions between Steve and Red escalate throughout the fight night. Red's overt partiality towards Harper, an old shipmate, during the match infuriates Steve further. Despite this, Steve wins the fight but not without a brawl with Red post-victory.

After the match, Steve encounters Laura Hopkins, a woman claiming to be pursued by the deadly Whang Yi society for a treasure map she possesses, a map to the hidden loot of the bandit Li Yang. Steve buys the map from her for fifty dollars, aiming to find the treasure himself.

Armed with the map and intent on treasure, Steve seeks to rent a motor launch from Chin Yat but discovers Red has already rented it. A confrontation leads to an agreement: they'll jointly seek the treasure but settle their personal feud after finding it.

The duo sets off, debating the map's directions and finally arriving at an island. After an exhaustive, grueling fight over who gets the treasure, they unearth the chest, only to discover it filled with machine gun cartridges instead of riches.

The treasure hunt turns out to be a scheme concocted by Suez Kit (Laura Hopkins), who sold fake maps to both Steve and Red, aiming to use their money to buy the real map. However, her plan is foiled when Smoky Harrigan and his gang steal the real map, only to be outmaneuvered by Steve and Red. Despite their efforts and the physical toll of their island duel, the "treasure" yields nothing but disappointment for all involved.

In the end, despite their ordeals and the lack of treasure, Steve and Red's rivalry remains unresolved, leading them to plan another bout to settle their differences.