I think I'll start at the end. Robert Louis Stevenson's last collection of stories was Island Night's Entertainments (1893). It contains just three stories, all set in the South Seas. "The Bottle Imp," a clever blend of Aladdin's lamp and a deal with the devil, might be Stevenson's most famous short piece. "The Isle of Voices" is similar, with a sorcerer replacing the genie. Both stories are nicely worked up, and follow their supernatural setups to logical conclusions. Honestly, they don't seem that special to me. Smart, imaginative, and professional - aren't those words of praise? They're good stories.
I thought "The Beach of Falesá" was a lot more interesting, and something new for Stevenson. In this long story (fifty pages or so), an experienced trader arrives at a new post in Polynesia and enters a duel to the death with a competing merchant. The rules in Polynesia are not those at home, and the white outsiders can change some of the rules. The Polynesians are both the objects of competition and self-interested players in their own right. Stevenson is satirizing English economic imperialism, but only up to a point. One of the traders is the hero of the story. He's telling it.
The narrator, Wiltshire, his voice - that's the core of "The Beach of Falesá." He speaks plainly, but with some first-rate metaphorical language, just enough to notice, but not so much as to render the voice false. He's a cynic and a realist, a cold manipulator, yet just a bit of a sap. He tells his story in an order that is logical for him, that is psychologically right - in order, but with digressions where they belong.
Wiltshire has just arrived on the island:
I had a glass or two on board, I was just off a long cruise, and the ground heaved under me like a ship’s deck. The world was like all new painted; my foot went along to music; Falesá might have been Fiddler’s Green, if there is such a place, and more’s the pity if there isn’t! It was good to foot the grass, to look aloft at the green mountains, to see the men with their green wreaths and the women in their bright dresses, red and blue. On we went, in the strong sun and the cool shadow, liking both; and all the children in the town came trotting after with their shaven heads and their brown bodies, and raising a thin kind of a cheer in our wake, like crowing poultry.
“By the by,” says Case, “we must get you a wife.”
“That’s so,” said I, “I had forgotten.” (Ch. I - even fairly short Stevenson stories frequently have chapters).
I think this covers a lot of what I see here. We have an ordinary simile in the first line, and an original one at the end, the poultry-like children. Wiltshire isn't afraid to look like a man of the world, and he does not apologize for the world that he finds himself in, however ugly. He might resist a bit - "I had forgotten."
If I have any doubts about Wiltshire's voice, it's in those metaphors. Sometimes, he's a bit too good. Mostly, though, he sounds like this:
She was the worst cook I suppose God made; the things she set her hand to, it would have sickened an honest horse to eat of; yet I made my meal that day on Uma’s cookery, and can never call to mind to have been better pleased. (Ch. II)
Stevenson has Wiltshire skirt right up to a cliché without quite using it, and then improve it just enough - the "honest" horse. The phrasing is conversational, too, which helps, such as making "the things she set her hand to" a separate clause, mimicking speech.
Stevenson's "own" voice, in his essays and travel books, sounds nothing like Wiltshire. The stuffy bachelor doctors in Dr Jekyll and Mr Hyde sound nothing like this. It's impressive.
I'm missing plenty, but I can't quite think of an earlier character quite like Stevenson's trader. He reminds me, strongly, of later narrators in Kipling or Conrad, characters who live in worlds that are strange and dangerous, characters who are not literary men but are still going to tell their stories. I don't think it's a matter of influence, since Kipling and Conrad were both writing their earliest fiction at almost exactly this time. I suspect that all three writers were learning how to adapt English fiction to a new kind of character, a new kind of story, to strip away some of the rhetoric that just seemed too false out in the colonies.
I have not emphasized that "The Beach of Falesá" is an adventure story, a good one. It ends with knives, guns, and explosions. You know that movie cliché where someone is shot and you think they're killed, but it turns out they were just hit in the shoulder, which is apparently a minor gunshot wound? That's here, so the device is at least 130 years old. Maybe Stevenson invented it. I doubt it.