People of the Book by Geraldine Brooks.
The last book I was so enamoured with that I forced myself to read it slowly, was The Thirteenth Tale, in late December 2006. People of the Book affected me in a similar manner.
There are two threads to the story:
A document known as the Sarajevo Haggadah, which disappeared in 1992 is believed to have been discovered, and a book conservator named Hanna Heath is chosen to assess its condition. She becomes almost obsessed with it, and we follow her as she journeys from her home in Australia to Sarajevo where the document is located, and to various parts of the world as she attempts to trace its origins.
The other thread, which begins with a young girl trying to escape the Nazis in 1940 and moves backwards in time to its creation in the late 1400s, traces the journey of the Haggadah itself through glimpses into the lives of its various possessors.
Both threads are absolutely fascinating, and I found myself a little frustrated each time the narrative moved from one to the other, because I didn't want the particular section I was reading to end.