Finity

From back cover Tor paperback December 1999:

VERTIGO!

Lyle Peripart's world is coming apart. Up to just a few days ago he was an obscure professor, quietly unenthusiastic about the Reichs that have dominated the world since the Axis victory over a century ago -- but not looking for a fight with anyone.

Then Lyle was recruited for private industry by the mysterious industrialist Geoffrey Iphwin -- and that's when everything stopped making sense.

His mild-mannered fiancee turns out to be a gun-toting weapons expert who grew up in a world in which America surrendered to the USSR in the 1970s. And several of their friends turn out to have grown up in different worlds still. Worse, they gradually realize that not one of them has ever talked to anyone inside the continental United States. In fact, just thinking about the United States is *hard* -- as if something is trying to stop them.

Something, in fact, seems to be trying to kill each of them. And Geoffrey Iphwin is trying to pull them together -- for a quest into what's actually going on.