Suppose you hopped into your time-machine, zipped backwards a century and landed smack on your great-great-grandpa, rendering him dead in the prime of bachelorhood.

Impossible?

Of course it is, for if you did that you couldn't be here to do that in the first place. Could you?

But suppose you found a crumbling letter, addressed to you, from your great (fifty-two times)-grandfather warning you that he was coming from the past to marry your fiance. You'd scoff, then wonder, then prepare to fight for the woman you loved.

And then you'd realize that if you won her you'd never be here to fight!

From Homer to Einstein, men have pondered the strange paradoxes of time and have wondered, "What if...?" Now, from the pyrotechnic pen of a science-fiction virtuoso, here are six dazzling ifs of time guaranteed to spin the hardest head. So read on, until tomorrow...or maybe yesterday.

Contains: "Rogue Star", "Dear Charles", "Dead City", "Sam, This is You", "The Other Now", "The Fourth-Dimensional Demonstrator", "The End"