In Jurassic time, when dinosaurs reigned supreme, an alien civilization of tiny micro-robotic natural historians arrived on Earth. Enmeshing the entire planet in a web of sophisticated sensors and using computer and information technology perfected over billions of years, they have recorded, catalogued, and studied everything that has happened since their arrival. Reclusive in the extreme, they have never interfered with Earth's history. Never until now. Matthew Crigler, a young professor of geophysics, is the first human to be directly contacted by the aliens. He becomes trapped in a strange plan to help them gradually introduce themselves to the human race. The power of the microrobots to acquire at will information about what is going on in homes, offices, and top secret government labs soon becomes apparent to Matthew. Their ability to make sentient virtual copies of life forms, including humans, brings into question the very meaning of life and death. The increasing awareness among humans that the past is not a matter of speculation and the present is without privacy leads to a series of social transformations that greatly alter the human race.