One of the best books I've read in a long time. If you're looking for a good read, I really recommend this.
Basic plot (as summarized by moi):
Sarah Starzynski and family are living in an apartment in Paris in July 1942 when she and her parents are taken by French police to a concentration camp in the middle of the night. In order to protect her younger brother from being taken by the police, she locks him a cupboard in their secret hiding place, not thinking she wouldn't be back to let him out.
American writer living in Paris with her French husband and daughter, Julia Jarmond is writing an article on the French roundup of Jewish families in Paris from 1942. By chance, she discovers that the the apartment she is in the process of remodeling and getting ready to move into was once that of Sarah Starzynski's family.
I won't give away any more details but this was a page turner and a great read.