Alex Hartdegen, a dedicated scientist residing in 1899 New York City, is captivated by the concept of time travel. As a professor of Applied Mechanics and Engineering at Columbia University, he often finds himself in hot water due to his avant-garde theories. He even corresponds with Albert Einstein, which showcases his intellectual ambitions. One fateful day, while on his way to meet his girlfriend, Emma, he becomes distracted by an early motor car. He swiftly helps the driver by activating the parking brake, thus averting a potential disaster.
Later, as he and Emma enjoy a romantic outing at the skating rink, he proposes to her, leading to a beautiful moment that takes a tragic turn. A robber suddenly emerges, brandishing a gun and demanding Emma's engagement ring. Alexander bravely intervenes, but the struggle results in a gun discharge, tragically leaving Emma fatally wounded in his arms. Devastated, Alexander dedicates the next four years to his laboratory, obsessively working on his time machine, a stark contrast to his once vibrant life. His isolation has caused a rift with his longtime friend, David Philby, who tries to coax Alexander back into the world by inviting him to dinner—an invitation Alexander keeps postponing, indicating that in a week they “wouldn't have had this conversation.”
With the time machine finally complete, Alexander sets out to change fate by traveling back to that fateful night four years prior. He intercepts Emma before she encounters danger, leading her away from the park to safety. Tragically, as he steps away momentarily to fetch flowers, Emma is struck by a horse and carriage startled by the very motor car that initially distracted Alexander. He realizes with a heavy heart that each attempt to save her leads only to a different tragedy, prompting him to plunge forward in time seeking answers.
As he ventures to 2030, he discovers plans for lunar colonization and seeks knowledge at the New York Public Library, where he converses with Vox 114, a holographic librarian. However, despite gathering information, he finds nothing helpful regarding time travel theory. Frustrated, he pushes further into the future, landing in 2037, only to witness Earth's devastation due to a lunar catastrophe. Narrowly escaping the chaos, he journeys through time and finds himself in 802,701 AD, where he encounters a primitive society of the Eloi, who live alongside a crumbling Manhattan.
As he navigates this new world, Alexander forms a bond with Mara, a teacher among the Eloi, and begins to uncover remnants of the vibrant civilization that once thrived. However, trouble soon finds them when Morlocks, monstrous predators lurking beneath the surface, launch an attack on the Eloi, capturing Mara. With the help of Vox 114, Alexander ventures underground to rescue her, only to be confronted by the Über-Morlock, who explains the temporal paradox holding Alexander captive. He reveals that Emma’s death is the catalyst that led Alexander to create the very machine he seeks to use to save her, and thus cannot change the past without the fate of Emma being entrenched in the timeline.
In a desperate bid to escape the Morlocks, Alexander commandeers his time machine, inadvertently dragging the Über-Morlock through time with him. After a fierce struggle, he ejects the creature from the time sphere, forcing it to age rapidly. Ultimately, Alexander’s journey takes him to a barren future over 635 million years later, where the world is dominated by the Morlocks, and he finally comes to terms with his inability to save Emma.
Resolute, he returns once more, this time to save Mara, jamming the time machine's controls to create a cataclysmic explosion that obliterates the Morlocks while allowing their escape. Stranded in the dystopian future, Alexander is determined to forge a new existence alongside Mara. He starts to reconstruct civilization, with Vox sharing the stories engraved in his memory with the Eloi. The poignant finale juxtaposes Alexander and Mara rebuilding life amidst ruins with a scene from 1903, where David Philby casually discusses with Alexander's elderly housekeeper, signaling the relentless passage of time and its everlasting impact.
