George Alec Effinger 
Bird of Time 

Far into the future, Hartsteins graduation present from his grandparents was a wonderful tripinto the past. He had a long future in the doughnut industry to look forward to but this trip was the icing on the cake. It had been a long time since that first experiment in time travel was successfully pulled off, although not without its flaws. Now, in the future, time travel was a lucrative tourist industry. But the time travel industry was keeping one little fact to itself: two percent never came back. This cover-up was the work of the Agency. The Agency knew what others did not: that the past wasnt really the past but a complicated dynamic of individual perceptions of what the past might have been. The past isnt real and reality becomes a state of mind. While selling their particular brand of escapist entertainment and vacation packages, the Agency didnt bother to tell its clients or the populace in general that a war was going on–a time war. The Agency was spending its time in a neck-and-neck battle with the Temporary Underground. The battlefield was none other than the space-time continuum, the weapons were time-shifts and theoretical mathematics. Hartstein had no idea what his trip would be or where it would take him.