This is the story of several archeologists who get the chance to
"go back in time" and basically become the fish out of water as a
battle is about to take place around a disputed castle in France
during the 100 Years War. Essentially, it's an adventure story, and
as such, it works very well indeed. It's difficult to put this book
down, and I read it very quickly and was sorry it was over.
In hindsight, however, there are a few problems. First is the fact
that the idea of time paradoxes (i.e. killing your own grandfather
so you couldn't have been born) is neatly dismissed early in the
book by using the multi-universe theory. However, multiple times
after that, time paradoxes are used and argued over. ARGH! Pick one
and stick with it! Less irritating is the stuff these people go
through in the scant 36-odd hours they have in the past (before
their machines run out of power and they're stranded). It's inhuman
the amount of energy they exert! Finally, there's the fact that
this book has the same plot as Jurassic Park: archeologists =
paleontologists, knights = dinosaurs, etc.
But if you don't think too much about it, it's a great book. I'm
sure it'll make a great movie as well. So, get it, enjoy the ride,
and don't let trivial things like time paradoxes upset you any more
than they would during a Star Trek episode or Terminator 2.