The book opens in a comfortable Victorian dining room, where a man the narrator calls the Time Traveller argues to his skeptical guests that time is simply a fourth dimension, no different in kind from length, breadth, and thickness, along which we might learn to move. To their disbelief he shows a small model that vanishes, and then the full-sized machine he has built. A week later he staggers in late to dinner, dirty and limping, and tells the story that fills the book.
He has driven the machine forward to the year 802,701. There he meets the Eloi, a beautiful, frail, childlike people who live among the ruins of great buildings, eat only fruit, and do no work. At first he reads their ease as the final triumph of civilization, a paradise where want and struggle have been abolished, and concludes that humanity has grown gentle and small because it no longer needs to be strong.
That hopeful reading collapses. He discovers a second race, the Morlocks: pale, ape-like creatures who live underground, tend the machinery, and shun the light. The Traveller comes to believe they are the long-descended children of the working classes, driven below by an ever-widening social gulf, while the idle Eloi descend from the rich. The old order has reversed: the Morlocks now keep the Eloi like cattle and come up in the dark to feed on them.
His machine has been dragged into the base of a great sphinx by the Morlocks, and recovering it forces him down into their tunnels. In the struggle he loses Weena, a small Eloi he had befriended, to a fire and the dark. Shaken, he climbs back onto the machine and presses still further forward, watching the sun redden and swell until he stands on a cold, silent beach thirty million years hence, where the tide has stopped and giant crabs and green slime are the last stirrings of life on a dying Earth.
He returns to the present and his dinner table, asking his guests to take the tale as a lie or a prophecy as they please, offering two strange withered flowers as his only proof. The next day he climbs onto the machine again and vanishes, and the narrator notes that three years on he has never come back. In an epilogue the narrator weighs the Traveller's bleak view, that civilization is a heap destined to fall back on its makers, against the small comfort that even at the end of man, tenderness survived.