The focus here is not time-machines as such but space-time paradoxes. Several stories deal with attempts to redirect the fickle finger of Fate--e.g., Fritz Leiber's whimsical fable of a homicide victim trying to rearrange matters with a temporal ""dispatching machine"" or Silverberg's own account of a luckless telephone caller who dials himself into a time-hopping war. In Marta Randall's ingenious ""Secret Rider,"" a woman rushes desperately between different spacetimes trying to find one in which she can bring an ampule of medicine to her fatally ill lover. Christopher Priest's ""An Infinite Summer,"" a beautiful story of ""time-freezing"" and an interrupted courtship, has already been introduced in Terry Carr's Best Science Fiction of the Year, No. 6 (p. 508), but it is more than welcome here. Funniest contribution: Peter Phillips' ""Manna"" (American miracle food gets shunted back to 12th-century monastery). Other excellent stories by Robert Sheckley, Poul Anderson, Roger Zelazny, A. E. van Vogt. A very agreeable anthology.