H.G. Wells' "The Time Machine" (1895)

The Time Machine was H.G. Wells’ first book, published in 1895 (with some parts appearing earlier in the National Observer and the New Review (Jan-May)). In it, the main character (addressed only as the “Time Traveler”) uses a homemade metal/crystal machine to travel about a million years into the future. There, he discovers that mankind has devolved into a pre-industrial, non-technological tribal civilization. He soon encounters two interdependent social groups: the predatory Morlocks and the innocently ignorant Eloi. 

(1st Edition)

Other stories of the 18th and early 19th centuries had also explored visions of the future ("Mellonta Tauta" (Edgar Allan Poe, 1849), "Looking Backward, 2000-1887" (Edward Bellamy, 1888), "With the Night Mail" (Rudyard Kipling, 1905)), but Wells’ book has pulp adventure and social allegory present in equal measure. In fact, his depiction of Earth’s fate in the Time Traveler’s second flight into the future is exceedingly bleak, and it’s imagery precedes the dystopic projections of much later authors such as Olaf Stapledon (First and Last Men) and H.P. Lovecraft ("The Shadow Out of Time"). 

For some reason, the book has appeared at various times as being divided into 12 (Heinemann edition), 14 (Holt edition) or 16 chapters. The below synopsis is based on the “official” 12 chapter version.

https://en.wikipedia.org/wiki/The_Time_Machine

Synopsis 

(illustrations by Jason Alexander from W.T. Robinson's 2013 abridged version)

1. One night during a weekly dinner engagement with scholarly associates, a man referred to as the “Time Traveler” describes the nature of time as the 4th dimension (beyond the 3 dimensions describing length, width and height). He presents a small ivory-crystal mechanism with a twinkling lever and describes it as a small time-traveling machine. After pushing a quartz lever, it disappears, supposedly into the future. He then shows them a large-scale version under construction with which he plans to travel through time.
   
2. The following week the Time Traveler arrives later to the gathering than usual, in tattered clothes and limping. After cleaning himself up a bit and satisfying a desperately voracious appetite, he begins telling a fantastic story which had begun earlier the same day, but had lasted a full eight days for the Time Traveler. The tale follows.
3. On the morning in question, the Traveler activates his machine and travels through a kaleidoscopic landscape of fast-changing scenery. When he stops the vehicle (now in the far future of 802,701), he finds himself on a hill on front of a marble, winged sphinx mounted on a room-sized pedestal. A group of small (somewhat elfin) men in tunics approach him from a nearby structure.
4. The Traveler befriends these small, virtually sexless future humans (the Eloi) and visits their large hall. He notices that there are no individual houses, only large, dilapidated structures sheltering groups of the Eloi. It seems to him that technological progress has driven out the need for man to struggle against nature, and therefore made him weak both physically and mentally.
5. The Traveler is horrified to learn that his Time Machine has disappeared, apparently stolen by an unknown agency and sequestered inside the pedestal of the sphinx. One day he saves an Eloi girl named Weena from drowning and becomes her friend. Around the same time, he catches glimpses of a member of a white-skinned, red-eyed, underground race named the Morlocks. The traveler theorizes that the Morlocks are descended from the industrial working classes of his own time, accustomed to living underground.
   
6. The Traveler decides that in order to regain his time machine he must investigate the underworld of the Morlocks. He descends a well leading to their realm. At first frightened, the Morlocks soon become more aggressive and try to capture him. He notices some half-eaten meat on their table, which is later revealed to be the remains of an Eloi. The horrified and weaponless Traveler barely escapes back up the well to the surface.
7. The Traveler realizes that the Eloi are essentially cattle for the Morlocks, bred in their large temple-like stables for food. The Eloi fear that with a moonless night approaching, the Morlocks will soon come for them. The Traveler notices a “Palace of Green Porcelain” several miles away and decides to make it into his refuge from the Morlocks. He brings Weena along with him for the journey.
8. The Green Palace turns out to be a ruined museum. Although there are signs of Morlocks dwelling in some of the lower parts of the museum, the Traveler finds a box of matches and makes himself an iron crowbar with which he plans to break open the base of the Sphinx (where he believes his time machine to be stored).
   
9. As Weena and the Traveler head through the forest back towards the Sphinx, the Morlocks attack en masse. In order to temporarily scare them off, the Traveler starts a forest fire. Nonetheless, the Morlock mob eventually sneaks up on him. Although the Traveler is briefly buried under a mountain of Morlocks, the rampant forest fire forces everyone to flee, until finally in the morning the Morlocks can only wander about blindly. Unfortunately Weena is nowhere to be seen, apparently a victim of the forest fire.
10. When the Traveler reaches the Sphinx, he sees that the door to its interior chamber is wide open and that his time machine is inside. As soon as he enters however, he realizes that he has fallen into a trap. The doors swing shut and Morlocks begin attacking him. In a final desperate scramble in the dark, he activates his time machine and escapes them, going farther into the future.
11. Going forward thousands and then millions of years, the Traveler sees the sun become a red giant which no longer moves across the sky. He halts the time machine’s progress and finds himself on a twilight beach facing a dead sea. When giant table-sized crabs begin to try and grab him, he barely escapes by again fast forwarding into the future. Several millennia later, the crabs are gone, only to be replaced by a tentacled, football-sized (or possibly bigger) blob.
    
12. The Traveler eventually returns back to his own time, and reunites with his dinner guests (who have been waiting for his entrance). The other men are mostly skeptical of the Traveler’s tale, even when he produces a flower from the future (which Weena had earlier slipped into his coat). The next day, one of the less skeptical of his friends (the narrator of the framing story) returns to find out more about the Traveler’s tale. The Traveler tells him that he is departing on another time trip, and that he will soon return with photographic proof of his travels. The narrator waits for the Traveler’s promised return (supposedly in half an hour), but now, three years later he has so far not reappeared.
    

• Epilogue: The narrator is unsure of where the Traveler may have ended up, and is not sure if the bleak future he described will come to pass or not. However, he takes comfort in that he still has the flowers Weena had given the Traveler, proof that some element of gratitude and tenderness may still persist in the future (this sentimental passage is not present in all versions of the book).