Reynolds, Alastair. Century Rain
Divergence: 1940 CE
What if: The German offensive through the Ardennes was halted, and World War II never happend.
Summary: A wormhole from our future leads to a 1959 Paris of what appears to be another timeline, in which two private detectives are trying to solve a murder.
Published: Gollancz 2004 (0575074361), 2005 (0575076917); Ace 2005 (0441012906BUY), 2006 (0441013074BUY).