Across Realtime pdf by Vernor Vinge
'The intricately plotted progress of characters from near to farfuture...on an Earth which, like an abandon playground, has long ago been left behind by an evolving humanity...human-scale action within a vast canvas' The Excyclopedia of Science Fiction. Encompassing time-travel, powerful mystery and the future history of humanity to its last handful of survivors, Across Realtime spans millions of years and isan utterly engrossing SF classic. 'You can hardly turn the pages fast enough. As sheer entertainment, it's a winner' Locus