Glen Cook 
Matter of Time 

May 1975. St. Louis. In a snow-swept street, a cop finds the body of a man who died fifty years ago. Its still warm.July 1866, Lidice, Bohemia: A teenage girl calmly watches her parents die as another being takes control of her body.August 2058, Prague: Three political rebels flee in to the past, taking with them a terrible secret.As past, present, and future collide, one man holds the key to the puzzle. And if he doesnt fit it together, the world he knows will fall to pieces. Its just A Matter of Time.