"A Sound of Thunder" concerns a group of hunters using a time machine to travel into the distant past, in order to hunt animals that are extinct in the modern era. In this particular case, they are hunting a tyrannosaurus rex, "the most incredible monster in history." However, little attention is given to building up the plot and rising action in anticipation of the dinosaur itself; instead, most of the focus is devoted to explaining the nature of time travel and the potential effects that actions in the past may have on the future.

The ostensible rising action and climax is the trip into the past, the appearance of the tyrannosaurus rex, and its death. However, the tyrannosaurus rex itself is ancillary to the main purpose of the plot, which is to display the effects that the hunters have on time as they know it. Even after the tyrannosaurus rex is dead, the action has not really abated; Eckels has made a mess of things, and the other hunters are now threatening to leave him behind in the past, almost certain that he has altered history. The return to their own time is something of an anticlimax; while Eckels did manage to kill a tyrannosaurus rex, he has no evidence of it, not even a photograph, and they still have to discover the effects that his actions had upon the timeline.

The falling action takes place between the time that the tyrannosaurus rex dies, and the hunters return to their own time. At first, Eckels and Travis seem too exhausted to quarrel, but then Travis realizes that Eckels has stepped off the path. He orders Eckels out of the time machine and threatens to leave him in the past, but then demands that Eckels fish the spent bullets out of the tyrannosaurus rex's carcass, though Lesperance suggests that this was unnecessary. Eckels passes out and seems to have thoroughly made a fool of himself.