Context

Written loosely in a third-person perspective, the novel is set in an alternative history of our world, shortly after Charles Darwin has published On the Origin of Species.^[5] A recent Russian influenza pandemic has just killed the British king and his next 137 heirs. Except for the opening chapter, the novel's action entirely occurs in the Great Southern Pelagic Ocean (the fictionalised South Pacific Ocean) on a particular island known by its indigenous inhabitants as "the Nation".

The first chapter involves a subplot in which the Gentlemen of Last Resort, a secret society serving the Crown, urgently set out for Port Mercia in the Great Southern Pelagic Ocean to seek the next man in the British line of succession: Henry Fanshaw, the unsuspecting governor of England's oceanic territories. Fanshaw's 13-year-old daughter, Ermintrude, is one of the novel's two protagonists. The other protagonist, Mau, is an aboriginal native of the Nation who is first depicted alone at neighbouring Boys' Island, where he has hand-built a canoe to complete his initiation rite from boyhood into manhood. Ermintrude, meanwhile, is travelling in a leisurely manner aboard a British schooner, the Sweet Judy, when mutineers, led by the ruthless First Mate Cox, are subdued and set adrift at sea, returning to the plot at a later time.

Plot summary

The main plot begins when an enormous tsunami carries the two central characters, Ermintrude and Mau, to the shores of Mau's home island: the Nation. Mau survives the tsunami in his canoe, while Ermintrude is the lone survivor of the Sweet Judy, which is run aground. The tsunami has killed all the indigenous villagers of the Nation, except Mau, who now angrily rejects the gods and believes that his interrupted rite of passage has left him soulless. Devastated, Mau carries all his people's corpses into the ocean, based on their religious belief that humans buried at sea become dolphins. Ermintrude timidly and sometimes recklessly interacts with Mau, but, eventually, the two start cooperating for mutual survival and establish some basic level of communication, though they are ignorant of each other's culture and language. Ermintrude introduces herself as "Daphne" and never reveals her given name, which she has always hated.

Three survivors from neighbouring islands arrive, including a cynical old priest named Ataba, who constantly derides Mau for his loss of faith. More survivors soon appear, including two brothers who can speak English moderately well with Daphne, speeding along the language-learning process for all. One of these men gratefully employs the reluctant Daphne as a makeshift midwife for his pregnant wife, Cahle. Meanwhile, Mau sleeplessly keeps vigil, obsessively looking out for local cannibals who are known to strike without warning. At the same time, he frequently hears the pestering, disembodied voices of the Grandfathers: ancestral spirits who make angry (and often incoherent) demands. They insist that Mau replace the "god anchors", carved white stones traditionally said to have "anchored" the gods before the tsunami displaced them. Mau discovers the anchors in the Nation's lagoon alongside an additional, previously unknown stone, but Ataba attempts to destroy it, purportedly because it is heretical. Mau then rescues Ataba from the lagoon, but his resulting hypothermia and exhaustion lead to a coma; Daphne accepts a lump of poison from Mrs. Gurgle, a shaman who is one of the refugees, that successfully lets her travel in her mind to the land of the dead in order to rescue Mau's consciousness.

Even more survivors have now arrived at the Nation, and Daphne begins hearing the voices of the Grandmothers, who claim to be the neglected but more sensible counterparts to the Grandfathers. They suggest that Daphne explore an ancient, closed-off crypt called the Grandfathers' cave. Mau, Daphne, Ataba, and their companions enter this cave and discover that the Nation is probably the oldest civilization on Earth, whose citizens once made astounding scientific progress with such creations as telescopes, eyeglasses, and even accurate star charts.

After exiting the cave, the group is confronted by two of Sweet Judy's villainous mutineers, who abruptly kill a spear-wielding Ataba and briefly abduct Daphne before she devises a cunning escape. In the meantime, the mutineers' leader, Cox, has since joined the cannibals, becoming their self-proclaimed chief and planning to raid the Nation. The new inhabitants of the Nation convince the arriving Cox and the cannibals to follow tradition by having the leaders of each side fight in hand-to-hand mortal combat, so as to avoid large-scale bloodshed. Mau accepts his role as leader of the Nation, and then cleverly outwits and kills Cox in the lagoon, causing the cannibals to flee.

A few days later, Henry Fanshaw arrives in search of his daughter. As a man of scientific curiosity, he, like Daphne, is fascinated with the re-opened cave. The Gentlemen of Last Resort appear two weeks later, telling Fanshaw that he is the next heir to the British throne and immediately crowning him king. Mau, wary of England's politics, is reluctant for the Nation to join the British Empire and instead requests that his homeland become a member of the scientific Royal Society. Ultimately, Daphne feels a duty to leave with her father, and Mau remains behind on the island with his new people.

Many years later, in the present day, an old scientist concludes this story to two children of the modern-day Nation. He explains that Daphne returned to England to marry a Dutch prince (later becoming Queen) and that Mau died of old age. When Daphne died, two months after Mau, her body was sent to the Nation to be buried at sea so that she could become a dolphin. He tells the children that from those days onward, thousands of scientists have visited the island, including Charles Darwin, Albert Einstein, Carl Sagan, and Richard Feynman. The book ends with the elder of the two children, a girl, standing guard on the beach, protecting the Nation as Mau had done so many years before: this is stated to be the Nation's new rite of passage into adulthood. In the lagoon, a dolphin leaps from the sea and the scientist smiles.