"Mary of Marion Isle"
The main character, the Hon Andrew West, is an eccentric young doctor, the nephew of a whisky baron, who has socialist views (rather like the title character in Marryat's "Mr Midshipman Easy"). He is in love with the shallow and vain (not to mention mercenary) Rose, who is daughter to his employer (he doesn't actually get paid), a Whitechapel slum doctor.
Dr West, who despite his eccentricities is quite capable, is taken on by a fashionable Harley Street society doctor (Dr Black), but is then sent to Egypt to accompany his cousin, the peer's heir. He has been sent abroad for his health, as he has consumption. Of course the cousin dies in Egypt, West returns home to find that Rose has married Dr Black (who has more money than she thinks Dr West will even have - she doesn't know he is nephew to a peer), and that the peer has died - leaving him now Lord Atterton.
Unfortunately, almost all the estate was left to his other cousin; Clara, as the old peer (who never liked him), thought that he was responsible for his son's death. He doesn't need to work as his cousin Clara has made him marry her, because she wanted the title (she is not shallow and vain like Rose, simply cold and calculating). West, now Lord Atterton, can't get a job as an ordinary doctor, because of his title. He dabbles in medical research (and becomes an FRS), tries politics (becoming Under Secretary for the Colonies), but leaves that.
Clara Lady Atterton arranges for him to be appointed Governor-General of Oceania (which they are happy to make him because of her money, and his title and political experience), but on the way out their ship hits an iceberg and sinks south-east of the Cape of Good Hope. Atterton and a clerk were busy with scientific experiments in the bowels of the ship, and a piece of iceberg prevented their escape when the others abandon ship. They eventually get out - after the ship begins to keel over the iceberg moves - and end up in a ship's boat. There is no sign of the rest of the crew and passengers, who have had to move away quickly for fear of the icebergs.
Fortunately, an albatross shows some interest in Atterton and his clerk, and they follow it for some hours, eventually coming to a miserable group of sub-arctic islands, which they conclude are the Prince Edward Group (which the captain had mentioned a few days earlier as being in the general vicinity). They land on one (they don't know which, but it turns out to be Marion Island - or Isle as it is called in the book). Thhey take up residence in a ruined hut they find on the island, which is fortunately well stocked with supplies for castaways.
After some weeks the clerk, who was injured leaving the ship, dies (although a doctor he is unable to operate because of an absence of equipment), and Lord Atterton is alone. He then begins to explore the island, and finds Mary. She was cast away on the island when 6, along with her ship's captain, who died some 6 years afterwards. She has been alone for 9 years, but is living quite comfortably. The albatross is, of course, one of her pets. She regularly converses with the dead captain, who told her that someone would eventually come to join her on the island. She also sees visions in a pool of water, one of which had shown her Lord Atterton's face. She of course doesn't tell him this at first, and indeed can't tell him very much at all for a while, as she has forgotten much of the English language since the captain died - though she kept up with her reading and writing - using a copy of "Whitaker's Almanach".
Andrew of course falls in love with Mary, who is far superior to either Clara or Rose, but is worried that Clara may still be alive. He decides to stay at the hut he first discovered, but collapses with pneumonia, and Mary nurses him back to health. Eventually he decides that he would rather spend the rest of his days with Mary on the island - but not before they make the mistake of sending a message placed around the neck of the albatross (something along the lines of "Lord Atterton, shipwrecked 'Neptune', on Prince Edward Group. Atterton").
The bird, irritated by the metal tag, dies on the coast of Western Australia. Eventually a prospector, looking for minerals, spots something metallic as he walks along a beach. Among the bone and feathers of the bird is the tag. Within days the papers are publishing the story that Lord Atterton, Governor-General designate of Oceania, did not drown on the "Neptune", as all had supposed - for the others had got safely to civilisation. of course the news was published the day after Clara's announcement of her forthcoming marriage to an elderly viscount - he wanted her money, she wanted his title. She had persuaded the court of chancery to presume Lord Atterton's death - which was not difficult, as the ship hadd sunk 6 years earlier, with him apparently trapped below decks.
Clara herself leads the rescue expedition, partly because she though that it would look good in the papers, and partly because she didn't want anyone else to find him. As she put it, he was peculiar before, after some years on an iceberg he would be mad. Because of Atterton's rank and importance, the navy dispatches a cruiser. The ship arrives off the islands, and discovers Andrew, Mary, and a daughter Janet (who was named after a daughter of Andrew and Clara, who had died).
Clara tells Andrew that it is his duty to return to England, and that she was obtained an assurance that he will be able to become Governor-General after all, as the man who replaced him is about to resign. However he refuses to leave, saying that he much prefers Marion Isle to London, and that he would never leave Mary. He necessary they would go the Canada, and build a home in some remote spot, but he didn't want to be Governor-General of anywhere but Marion Isle.
Clara tells Mary that Lord Atterton will be ruined if he doesn't return to civilisation, as he is a great peer with a social and political position to uphold. Mary, knowing that Andrew would never leave her voluntarily, decides to drown herself, thinking that this would be best for Andrew. Clara realises that Mary has this intention, but doesn't say anything because, from her point of view, it was the most efficient way out of a difficulty. However, as Mary attempts to carry out her intention, Clara, who is in a ship's boat come to fetch Andrew, by force if necessary, is lost overboard when the boat is capsized by the strong currents. Mary tries to rescue Clara, but she fails.
The three of them remain on the island.
This is a curious work, effectively in two parts, Britain and Marion Isle, a small island in the sub-Artic regions. The first part is Victorian melodrama (curious enough, given that the book was actually published posthumously in 1925. There is no clear indication when it was set, though there is mention of horses and carriages, no cars were mentioned, that I can recall. However, it does refer to the ship sending out an SOS, so it is probable it was set when written, presumably the early 1920s.
The second part is sub-Defoe, or "Swiss Family Robinson". A curious mix. Not particularly realistic, however, even for a Haggard novel. The idea of the eternal triangle is, however, a theme which surfaces in a number of other Haggard novels, including "Montezuma's Daughter" - with which there are some similarities - and Alan Quartermain also finds himself in this position.
Marion Island is 2,300 km SE of Cape Town (I didn't find the distance in nautical miles), so I wonder whether a ship would be likely to be travelling anywhere near it - and I recall that the ship actually sank some hundreds of miles south of the group. Andrew Lord Atterton had found a wild cat, and tamed one of its kittens, which is interesting as I see that South Africa introduced cats in 1949, and there grew in number until there were 3,400 by 1977 - they have since been exterminated. I wonder whether the South African weather station live on the same diet as Mary - penguin eggs, fish, Kerguelen cabbage, and the cultivated crops which derived from the horse feed the ship had carried?