STEVENSON has sometimes been dismissed as “merely” a writer for children but The Strange Case of Dr Jekyll and Mr Hyde is a moral fable of an entirely adult character. For all its sensational success and longstanding popularity in multiple versions in a variety of media, it is in Henry James’s words, “the most serious of the author’s tales” – a story whose seriousness resonates with ever more sinister conviction. The work is made up of different written accounts by various characters: an unnamed narrator, Mr Utterson the lawyer, Mr Enfield the man-about-town, Dr Lanyon and Dr Jekyll himself. Each partial perspective casts a different light on events.

A mysterious, dark and evil-looking figure is seen in London. This person is tracked to Dr Jekyll’s home, confronted by Utterson, but his identity not disclosed. He is seen killing a young girl, trampling her to death; a maid glimpses him; the mystery gathers. Everything builds to the final section, “Henry Jekyll’s Full Statement of the Case” where the proposition from which the whole story has developed is revealed: Dr Jekyll says that he began with the conviction “that man is not truly one, but truly two” and that later, others may go even further, and discover “that man will be ultimately known for a mere polity of multifarious, incongruent and independent denizens.” But meantime, his own “two natures” were bound together “in the agonized womb of consciousness” and that these “polar twins” were condemned to be “continually struggling.”

And Hyde hates Jekyll. Driven by fear of the gallows, he returns to his “subordinate station of a part instead of a person” to occupy the body that once was wholly his own. He loathes this necessity and resents Jekyll. When Jekyll writes his final account, he knows that the chemical potion he has taken to keep Hyde at bay, within himself, will lose its effect. Hyde will return. His only solution is suicide: “this is my true hour of death, and what is to follow concerns another than myself. Here, then, as I lay down the pen, and proceed to seal up my confession, I bring the life of that unhappy Henry Jekyll to an end.”

The seriousness of the argument that runs so urgently through the whole work increases in intensity and pathos, and grows with each new reading. The argument is that duality, even multiplicity, of identities, in a singular human self, is not to be tolerated by the priorities of science. Science wants things neat and fixed in categories. You are a sole commodity, a unit to be dealt with. Yet every human being knows the complex, shifting selves that make the self, make any one of us who and what we are. Many make one. And one among many creates the polity of selves called society. Alienation from separate selves and isolation in the city, make the choice of London as location frighteningly apt.

Stevenson’s work is shocking, indeed, but it prophecies major trends in the history that followed it: the exaggerations of violence in the service of childish appetites, the indulgence of vanity at the expense of good reason, the centring upon the self, legitimising greed, self-righteousness, and physical might, at the expense of social contact, admission of complexity, openness to difference and change. Stevenson knew bad weather was ahead.

The quality of conflict between inflexible power and the necessary forces of change informs the fragment of the novel he was working on at the time of his death, Weir of Hermiston (1896), an exploration of the relation between an authoritarian patriarch and his free-spirited son, where the language of many of the most vivid characters is a rich vernacular Scots and the characters themselves – women and men – are among the most memorable Stevenson ever created.

Stevenson’s most famous travel books, novels, short stories, poems and his letters also show the range, insight and quality of his writing. His fiction is linked in one specific way to the Scottish tradition, back to James Hogg and Walter Scott (and further back, to Robert Henryson’s Fables) and forward to Muriel Spark, James Kelman and Irvine Welsh (and thinking of Hawthorne and Melville, to American literature as well): this is the literary device of the “unreliable narrator”. Iain Banks began his novel Transition (2009) with the sentence, “Apparently I am what is known as an Unreliable Narrator, though of course if you believe everything you’re told you deserve whatever you get.” When we consider Stevenson’s stories, however, there is a specific historical moment that must be taken into account. Hogg, Scott and Stevenson all grew up in a Scotland where oral storytelling was a common currency. Hogg and Scott were pioneers in the work of recording and writing oral stories, songs and ballads. Something very particular in written narrative is happening in this transitional overlap between the literary artifice of these writers and the oral traditions they experienced, and Stevenson’s experience of oral storytelling culture was expanded in the South Pacific islands and especially Samoa.

An excellent essay that opens up questions about this is Walter Benjamin’s “The Storyteller” (1936) easily available in the collection Illuminations. In Hogg’s novel The Confessions of a Justified Sinner, the ambivalence of either a rational or a supernatural explanation of events sustains tension, as the narratives – plural – of the novel reveal themselves. In Jekyll and Hyde, the multiple narrative perspectives delivered in different forms of written address help create an equally effective tension. Something similar happens in The Master of Ballantrae (1889). What seems certain becomes increasingly questionable. The principal narrator, the factor Mackellar, seems to be a reasonable and reliable witness, but Stevenson is assiduous in indicating that there is more to it than that, and if the sinister figure of Secundra Dass takes the role of the familiar companion to the ostensibly “evil” James, Mackellar stands in the same relation to the ostensibly “good” Henry. So the tale of the two brothers Durie is far from unambiguous.

In his shorter fiction, the matter of ambiguity presents itself most forcefully both in the way the narratives are disclosed and in the palpable physicality of the language – or languages – in which they are written.

“Thrawn Janet” (from The Merry Men & Other Tales) is a good place to begin. The basic trope of the story is that a minister who thinks he knows what’s what, is confronted with inexplicable realities. The story begins in the minister’s English language, suggesting a formal, logical, ecclesiastic or legal mind at work. By the end of the opening section, though, we are in “an atmosphere of terror” and the story now immerses the reader in the Scots language, close enough to English to be easily readable but different enough to make the experience strange. The unknown, violent, distorted, devilish parts of the world wreak revenge upon the Minister’s self-righteous sense of order and the justness of things in what he believes is God’s universe.

Other stories of immediate appeal include “Markheim”, a Dostoevskian vignette on the meaning of good and evil, “A Lodging for the Night: A Story of Francis Villon” (from New Arabian Nights), depicting medieval winter in Paris, “The Bottle Imp” (from Island Nights’ Entertainment), a version of the Faust story with a happy ending, and “A Fable: The Persons of the Tale”, an “interruption” to Treasure Island, ostensibly taking place between chapters 32 and 33, where Captain Trelawney and Long John Silver have a conversation, Silver confidently asserting, “If there is a Author, by thunder, but he’s on my side...”

Stevenson was keenly attuned to the dynamics of the late 19th century that were to generate what was to follow, but in the 1920s, they had to be rediscovered. The biologist, town-planner and social visionary Patrick Geddes had heralded what he called an approaching “Scottish Renascence” in the 1890s but it took a while to arrive. The First World War of 1914-18, the Easter Rising in Ireland in 1916, the Russian Revolution in 1917, all blew apart the imperial certainties and authority of British monarchical rule upon which the 19th-century empire had been built.

Stevenson, hypersensitive to the attractions and compulsions of evil, keenly aware of the vulnerabilities of virtue, knew exactly what humanity is capable of. His work is as vital now as it was a century ago.

[Boxed off:]

This is Mackellar’s view of the Master of Ballantrae in Chapter 9 and shows the ambiguity of the figure literally ascending and descending in a constantly shifting perspective. They are on board the ship aptly named Nonesuch, crossing the Atlantic, and the sea is rising and falling:

Now his head would be in the zenith and his shadow fall quite beyond the Nonesuch on the further side; and now he would swing down till he was underneath my feet, and the line of the sea leaped high above him like the ceiling of a room. I looked upon this with a growing fascination, as birds are said to look on snakes... [The Master’s] tale, told in a high key in the midst of so great a tumult, and by a narrator who was one moment looking down at me from the skies and the next peering up from under the soles of my feet – this particular tale, I say, took hold upon me in a degree quite singular...