On January 5, 1900 in London, four friends arrive for a dinner at the house of their friend H. George Wells (Rod Taylor), an inventor. Bedraggled and exhausted, George arrives and begins to describe the strange experiences he has had since the group last met.
At their earlier dinner, on December 31, 1899, George describes time as "the fourth dimension" to David Filby (Alan Young), Dr. Philip Hillyer (Sebastian Cabot), Anthony Bridewell (Tom Helmore), and Walter Kemp (Whit Bissell). He shows them a small model of his time machine and asks a guest to press a tiny lever. The device disappears, validating his claim, but his friends remain unconvinced; their reactions vary from curiosity to frank dismissal.
George bids his guests a good evening, then heads downstairs where his full-size time machine awaits. He presses a lever and moves forward through time 17 years into the future. He meets Filby's son, James, who tells him of Filby's death in the Great War. Saddened, he resumes his journey, stopping in 1940 during The Blitz, finding himself in the midst of "a new war"; George resumes his journey and stops in 1966, finding his neighbourhood now part of a futuristic metropolis. People are hurrying into a nearby fallout shelter amid the blare of air raid sirens. An elderly James Filby urges George to immediately take cover, but he does not understand the danger. A nuclear explosion causes a sudden volcanic eruption around him. George continues his journey forward as the lava rapidly cools and hardens, trapping him inside. He travels far into the future until the topography changes. Hundreds of thousands of years later, the rock erodes away to reveal that London is now gone, and has been replaced by a lush, green and unspoilt landscape.
George stops in AD 802,701 near the base of a towering sphinx. He goes exploring and finds a group of delicate young men and women wearing simple clothing gathered at a stream. One woman, carried off by the current, screams for help but none of her companions show any concern. George rescues her and is surprised when, revived, she walks away without a word; later, she seeks him out, giving him a flower. She says her name is Weena (Yvette Mimieux) and tells George her people are called the Eloi. He soon learns the Eloi do not operate machines, work, read, and know virtually nothing of history; they do not even understand fire.
George decides to leave but discovers his machine has been dragged into the sphinx. Weena tells him "Morlocks", who only come out at night, have moved it. A Morlock jumps out from behind bushes and tries to drag her away, but the creature's light-sensitive eyes are blinded by George's fire torch; he easily rescues her.
The next day, Weena shows George domed, well-like structures that dot the landscape; they are air shafts that double as access to the Morlock underworld. She takes him to an ancient museum where "talking rings" tell of a centuries-long nuclear war in the distant past. A reduced population fought for survival in the poisoned landscape; many decided to live underground in permanent settlements, while some decided to return to the surface. George realises this marked the beginning of speciation for the Morlocks and the Eloi. He starts to climb down a shaft but turns back when sirens blare from atop the sphinx. He emerges to find Weena gone and crowds of Eloi in a trance-like state, entering open doors at its base. The sirens stop and the doors close, trapping Weena inside.
George enters the Morlocks' subterranean caverns and is horrified to discover that the Eloi are the free range livestock for the cannibalistic Morlocks. After finding Weena, he begins fighting the creatures. His efforts inspire other Eloi, who begin to defend themselves. George sets a fire and urges the Eloi to clamber out of the caverns to the surface, where he directs them to gather dry tree branches and drop them down the shafts. Smoke billows out of the shafts, and the subterranean cavern later collapses.
The next morning, George finds the sphinx in charred ruins and its doors open. His time machine sits just inside, a trap set by the Morlocks. He enters, the doors close, and he is attacked in the dark. George sends his time machine hurtling into the past, returning to 1900. It comes to rest on the lawn outside his house, where his story ends.
George's friends are again skeptical. He produces Weena's flower and Filby, an amateur botanist, says the species is completely unknown in the 19th century. George bids his guests a good evening. Filby steps out but returns to find George and his machine gone. He notices drag marks where it would be positioned outside the sphinx after returning to the Eloi. Filby and Wells' housekeeper notice three books are missing. Filby asks her, "Which three would you have taken"? She wonders if George will ever return. He observes that George has "all the time in the world".
Output: How far into the future must George go before the lava turns into a lush green landscape?