The year is 2055. Time Safari, Inc. offers its clients the chance to travel to the past to hunt prehistoric animals, such as *Tyrannosaurus rex*. Anything goes, provided one does not stray from the designated path... This masterful story -- which gave rise to the "butterfly effect" theory -- deals with time travel and its consequences for the future, but above all, it prompts us to reflect on how our actions affect the world around us. *Locus*, the prestigious science fiction magazine, regards this tale as the most significant in the history of the genre.