Go backward through space-time into prehistory? It seemed fantastic, but the machine — invented by Bob’s father in connection with his research on the interrelation of time and gravity — actually existed. Bob and his friend Pete are anxious to be the first to visit the era of the dinosaurs. Overruled, they watch Pete’s father, a famous paleontologist, step into the shimmering ring — and disappear into the past. But when he does not return on schedule because the machine jams, Bob and Pete follow on a daring rescue mission…
A thrilling time-travel adventure as only master storyteller Lester del Rey could tell it!