The small European population of the island of Mayou, off the coast of Papua New Guinea, is intrigued to see a yacht approaching the island. The two passengers appear to be respectable 'gentleman', but the trader Blount soon recognises the captain of the ship as one Captain Sykes, a notorious blackbirder who has served time in prison in Sydney for his activities. The chief of the island, Banderah, has his own grievance against Sykes and plots revenge. Blount uncovers a conspiracy between the visitors and the other two traders living on Mayou and he and Banderah devise a scheme to expose them. However, the plan goes hideously wrong and leads to bloodshed and death.
Meston narrates this story as an observer who travels to High Island, the Aboriginal 'Caparra,' in the Frankland Group near Cairns, with his Aboriginal friend Milbirrie and two Chinese. There he meets a man who is testing the faithfulness of the woman he loves by asking her to stay with him alone on the island for a month. Suspense arises over whether the woman will pass the test. Then the man plans to '"take her back to Sydney and make her my wife, in deference to the most baneful misery creating custom that has ever cursed the human race." Such was his complimentary reference to the law of marriage.' When the woman passes the test, the triumph of love is signalled by a 'glorious rainbow' visible from the island at the north peak of Bellenden Ker: 'A bridal veil from the great "Twin Sisters" to the bride on the coral strewn shore of green Caparra!'