The Difference Engine is a 1990 alternate history novel written collaboratively by William Gibson and Bruce Sterling. It is a prime example of the steampunk sub-genre, often considered the Genre Popularizer.It posits a Victorian Britain circa 1855 in which a great wave of technological and social change has occurred after entrepreneurial inventor Charles Babbage succeeded in his ambition to build a mechanical computer (actually his analytical engine rather than the difference engine). Among the many various changes that arise as a result of this innovation are an even more powerful British Empire, a Divided States of America, an early Communist Revolution in Manhattan led by Karl Marx himself, steam-powered gurneys (this timeline's equivalent of cars), and the premature invention of "camphorated cellulose" (what we know as plastic).The story follows Sybil Gerard, a political courtesan and daughter of an executed Luddite leader (she is borrowed from Benjamin Disraeli's novel Sybil); Edward "Leviathan" Mallory, a paleontologist and explorer who comes into a lot of money thanks to a good bet on an advanced steam gurney model; and Laurence Oliphant, a historical figure with a real career, as portrayed in the book, as a travel writer whose work was a cover for espionage activities "undertaken in the service of Her Majesty".Linking all their stories is the trail of a mysterious set of reportedly very powerful camphorated cellulose computer punch cards and the individuals fighting to obtain them; as is the case with special objects in several novels by Gibson, the punch cards are to some extent a MacGuffin.
Chekhov's Gun: Mallory notes an Awesome, but Impractical 'machine-carbine' which is rather inaccurate; at the end of his story Captain Swing empties a magazine from one at him, only to miss completely and fall to a single aimed shot from Mallory's buffalo rifle.
Coitus Ensues: Mallory abruptly has a romantic fling with Hetty, going so far as to abandon the recently injured Ebenezer Fraser to do so. This detour is largely why he gets trapped in London in the wake of the riots.
Dark Secret: Sybil hints in the final chapter the assasination of the Duke of Wellington had been instrumented by the Rads themselves and performed by the Brotherhood of Sappers and Miners. Cue the said Brotherhood to be the wealthiest workers' guild through the next 2 decades, always getting the best public works contracts and being most leniently treated when they do a strike...
Dirty Commies: The Manhattan commune, lead by noone else but Karl Marx
Red Scare: Subverted and ridiculed to death - the speeches of the revolutionary Marquess and Captain Swing himself are deliberately out of touch with reality: no sane man would listen to a Communist-anarchist who owns Black slaves, the working classes would not be interested to support Communism if they have careers to upheld and "brotherhoods" to protect themselves (the supporters of the revolution are mostly thieves and bandits), the idea that "evil capitalists" would gladly shoot human hostages and protect the goods in the warehouse proves to be just as idiotic in-universe as anyone would think, "the temperance speaker" is a murderer herself.
Divided States of America: The CSA became independent, as did Texas, California, the Manhattan commune, and Britain is playing "divide et impera".
Emperor Scientist: The merit Lords, including Brunel, Darwin, Babbage and several other famous Victorian scientists.
Also Aristocrats Are Evil: The Radical Party removed the old aristocratic class from power and eliminated the ancient titles of nobility, replacing all of them with "Lord", be it by birth or by merit.
Fanservice: in-story. The clock Mallory buys has an allegoric depiction of Science, Progress and Britain. The latter is, for some reason, wearing almost nothing. Other examples include the americans' theatre and the artists on Montmartre (described as "dressed... erm, undressed similarly to each other").
Since it's Victorian England, wearing a skirt so short it shows one's lower leg when she bends over is treated in-story like if she wore a mini-skirt that doesn't cover her panties.
Deliberate Values Dissonance: Sterling and Gibson jump from allusions to female scientific (Lady Ada) or craftsman's (seamstresses to Engine-punchers) careers to the fact it was scandalous for an unescorted woman to ride the subway - which is at the same time uncanny and even worse when one thinks of certain Middle Eastern countries...
Fictional Political Party: The Industrial Radical Party, who believe in scientific endeavor, industrial progress, and meritocracy, appointing peerages to "savants".
Footnote Fever: to let the average writer read the book properly without wondering "Who the hell are those people?!"
Forbidden Fruit: The sheer possibility of receiving a fellatio makes Mallory shiver with delight after all the fantasies about it.
Good People Have Good Sex: Kind of. Lord and lady Byron have BDSM sessions and so on, while Mallory and Hetty had a very romantic night. On the other hand, Mallory's night with an Indian widow is very much Fan Disservice, for himself included.
Hand Cannon: Brian's "not exactly regulation" Russian pistol.
Hold Your Hippogriffs / Call a Rabbit a "Smeerp": Many modern concepts are expressed through real and made up XIX era slang. "Clackers" instead of "hackers" with cyberpunk-like genre built around them; kinotropes instead of movie projectors, television, rotating billboards, etc.
Hooker with a Heart of Gold: Cybil and Hetty, albeit in different ways. Cybil'd been forced into that lifestyle and quit it as soon as she got the chance, Hetty is easy-going, very much enjoys sex (something that almost never happens with prostitutes) and is into prostitution only because it pays okay, unlike singing / dancing / posing which she also dabbles in.
Inferred Holocaust: the steampunk dream of a Victorian information age is somewhat deconstructed by the heavy hints that they're using it to catalogue people for the purposes of the then-popular doctrine of eugenics. The ending (set in the 1990's) implies that humanity only exists as simulated information.
Libertarian Socialism: The solution to the worker vs state clashes of the Real Life 1830s was to let the trade unions evolve into uniformed guilds ("brotherhoods") which own property, tooling and industrial patents and which hire their men (with skills and tools) to businesses for significant amounts of money.
Jive Turkey: Sterling and Gibson go to great effort into fitting the British slang of the time into the story, an effort which might have been wasted:
"Sand-hog" for underground construction worker is an American slang word first heard in the 1870s.
"Dollymop" for prostitute is a late 19th century word.
"Navvy" for road construction worker is a 20th century word, in the 1850s it designated a railway or canal construction worker.
People's Republic of Tyranny: The Government claims to be liberal, in practice it holds files on most citizens, blackmails, hangs political opponents and asks from everyone, Mallory included, to declare publicly their allegiance to the party.
Pretty Fly for a White Guy: The Japanese quartet can be described as extreme reverse weaboos, since they love everything western so much they want to get rid of the Japanese language.
Schizo Tech: Played realistically. Tom and Brian Mallory built a racing steam-car in the shape of the 1930s streamlined racing cars, but due to the huge fuel consumption of steam engines they needed to take a coal wagon in tow to drive from Sussex to London. Even the most primitive gasoline engines in Real Life only took a couple of gallons of fuel for the same route.
Unperson: Erasing people from the database does more or less that. Subverted in that it's a good thing for some (Sybil started her life anew, for one), though it's still an effective threat for law abiding gentlemen.
What If? ...Charles Babbage had completed his Difference Engine (and gone on to build the Analytical Engine)?
Witch Hunt: The hunt for 'Luddite conspirators' by Charles Egremont.
Woman Behind The Man: Lord Byron, dashing hero and exceptional public speaker, is uncovered in the appendices after his death as a rather incompetent administrator, pushed and manipulated in political decision by Lady Annabella Byron, who rants on having to endure "his beastly habits" for decades. Victorian Age being what it was the position brought little profit to her.