Finity — John Barnes

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.