A consultant finds a fossilized pack in the desert, then finds himself back in the Miocene with a criminal gang. A game warden busts a group of trespassing druids in a wildlife sanctuary. They vanish in a green flash and he loses his job, only to be recruited for something much bigger. This is the big secret: time travel is easy. There are over four billion years in Earth's past. The deeper one goes in time, the more alien the Earth is. Still, people have settled most of Earth's history. Of course they live without a trace, for that is the law of deep time. To do otherwise could create paradoxes, bifurcating histories, even time wars and mass extinctions. Where there is law, there is also crime. When crimes span millions of years, law enforcement takes a special kind of officer. An ex-game warden can be the perfect recruit. At the right time.