The story discusses the slave labour trade in Australia, when labour was poached from the Solomon Islands. Captain Birtle returns to an island called Namuka, where he has an agent, Samoan Tom, stationed to procure trading goods. Tom, due to an inebriated episode, has been killed and eaten by the local islanders. Captain Birtle stays at the post to procure more trade goods and sends his schooner back to Australia to return when he has more items to trade. During his stay he discovers a local who has found a shipwreck that contains gold coins. Through long negotiations Captain Birtle is taken to the location and begins to obtain as much gold as he can. The more money he collects, the more fearful he becomes for his safety. He writes a letter to his sister informing her of his hoard and instructing her how to access it if he is killed.
His two nephews, Mark and Harry Derrison, travel to Australia to trace the treasure. On the boat they incautiously let slip the reason for their visit. On arrival in Melbourne, one of their fellow passengers steals the Derrisons' trunk and heads off to Sydney from where he can start an expedition to the islands. The two brothers follow. They take up a place on a labour recruiting ship, although they are first concerned about the ethics and morality of 'blackbirding'. Their fears are quelled by the Captain, but during the journey they witness many atrocities performed against the islanders and they take a moral stand. The brothers are dropped off at Namuka, and are greeted by a new storeman, Judd Gridley, who knows their uncle. Gridley tells Mark and Harry that two men claiming to be Captain Birtle's nephews arrived earlier. Knowing it was Snape and Mudge, fellow passengers from their journey over, Mark and Harry devise a plan to claim what was theirs. They manage to reclaim the treasure and find their uncle, who has been taken captive by a neighbouring tribe. With the profits from their treasure, they offer Judd a part in the trading business and the four return to Australia. The story has a strong anti-slavery message.
