The story follows a group of scientists, two geologists (Barton and Davis) and a palaeontologist (Fowler), who are excavating dinosaur footprints. They come across two physicists (Barnes and Henderson) who are investigating a strange liquid that exhibits negentropy, which Davis describes as being akin to "Time's Arrow" as "Any clock you care to mention – a pendulum for instance – might just as easily run forward as backward. But entropy is a strictly one-way affair – it's always increasing with the passage of time. Hence the expression, 'Time's Arrow'". This causes the realisation that negentropy could result in a reversal of time.
Fowler is invited to visit Henderson's lab, during which time the two geologists come to believe that the physicist is trying to effectively build a way to view the past firsthand. Henderson confirms their conclusion and asks Fowler to join him during the machine's first test run. The dig continues and the team discovers that the footprints give off the impression that the dinosaur was chasing something. Fowler sets off for the lab via Jeep, shortly after which Davis sees the lab explode and the surrounding area ripple. He returns to alert Barton, who has discovered that the dinosaur tracks are accompanied by Jeep tyre prints, implying that the dinosaur had chased after and subsequently trampled Fowler.