Timeline - Michael Crichton Techno/historical adventure from Michael Crichton, taking place in 1990's America and mediaeval France.
Without giving too much away, a group of archaeology students are sent back in time to rescue their professor who has got stranded there.
As with most Crichton books, it reads like a screenplay, keeping the plot moving between different characters and places.
The story is different enough from the film that did eventually come out to the extent you can read the book without spoiling the film (or vice versa).