In the year 2055, Mr. Eckels enters the office of Time Safari, Inc. This company offers safaris to the past in order to hunt dinosaurs and other large prehistoric animals. Eckels greets the company official, who informs him that there are no guarantees that he will come back alive.
While waiting for his safari guides, Eckels makes small talk by expressing his relief that Keith was victorious in the recent presidential election. The official agrees that Keith is the best candidate for American and democratic values, asserting the Deutscher would have brought about a dictatorship. Eckels takes another moment to reflect on the danger of the expedition, hands over his check, and departs with the safari guide Mr. Travis.
Eckels settles into the Time Machine alongside Travis, fellow guide Lesperance, and two other hunters. The Machine blazes back through time as the travelers get settled with oxygen helmets. Eckels nervously contemplates the rifles they all hold, and eventually the passengers find themselves in the prehistoric past.
Upon descending from the Machine, Travis emphasizes that the travelers must not disturb the natural environment. He exhorts the hunters to stay on the metal Path that hovers over the ground in order to prevent stepping on any plant or animal. Crushing even the smallest life form, he explains, could disrupt ecological balance and change the future, not just of nature, but of human society. Lesperance explains that the party can safely shoot the specific animal he has previously marked for them, because he has already traveled back in time to find a creature that would die of some accident anyway and looped back to mark it with paint. Eckels asks him whether their hunt will be a success, but the guide explains that there is no way to know because one cannot meet oneself while traveling through time.
Soon the Tyrannosaurus Rex approaches with a sound of thunder. Eckels is transfixed when he comes face to face with the massive creature, proclaiming it impossible to kill and that he wishes to retreat. Lesperance directs him to wait in the Time Machine. Instead, dazed, Eckels wanders off the past while the other hunters shoot and kill the fearsome dinosaur.
Travis returns to find Eckels in the Time Machine. Realizing that Eckels wandered off the path, Travis yells that his transgression could ruin the company and threatens to leave him behind. He eventually orders Eckels to retrieve the bullets from the carcass. When Eckels returns, covered in blood, they leave for the future.
When they arrive, Travis orders Eckels to leave and never come back. Eckels, however, lingers for a moment, noticing that the atmosphere and small things about the office have changed. He slumps down into a chair and, examining his boots, finds that he has crushed a butterfly. Panicking, he asks the official about the election results and learns that Deutscher has won. After a few moments of pleading to go back and fix things, Eckels waits in silence while Travis aims a gun at him. Eckels hears Travis click the gun’s safety, followed by a sound of thunder.