Across Realtime by Vernor Vinge
Previously published in three parts, The Peace War, Marooned in Realtime, and The Ungoverned, this is a marvelous extrapolative tale, to which no summary can do justice, with a gripping blend of high-tech razzle-dazzle and good old-fashioned murder mystery–all spiced with . . . the time-travel theme.–Kirkus Review.