Was this ill-fated expedition the end of a proud, old race-or the beginning of a new one? There are strange gaps in our records of the past. We find traces of man-like things-but, suddenly, man appears, far too much developed to be the 'next step' in a well-linked chain of evolutionary evidence. Perhaps something like the events of this story furnishes the answer to the riddle.

Reach into the distant past and discover the fascinating origins of the advanced technology that allows future Earth inhabitants to journey between parallel universes at their whim. This entry in H. Beam Piper's popular Paratime series homes in on the Martian colonists who visited Earth hundreds of thousands of years ago.