In 1912 the entire continent of Europe was replaced. The new continent is similar, geographically, to the old, but completely devoid of any humans or even Earthly creatures.
In the wake of this catastrophe, history has changed quite a bit - the economy has issues and religion has taken over in a lot of ways. By 1920 humanity is making a dent into the dangerous lands of Darwinia. Guillford Law (I hope I spelled that correctly, the book isn't here with me), a photographer, is heading into uncharted lands with an expedition that ends up revealing more than he could ever imagine about what happened on that fateful night in 1912.
The book changes. Don't buy it if, strictly enough, you're looking for a book just about this. If you've read some of Robert Charles Wilson's other books and liked them then you'll be more likely to like this book.
I personally enjoyed the heck out of it.
(I'm not even going to really tag this book like I do most books to help preserve anything else about it. I hope I haven't given away too much as it is...)