Sarah's Key weaves two stories, one of a young Jewish girl whose family was arrested during the Vel' d'Hiv roundup in France, an event not well known (or well publicized, for obvious reasons) even among the French. As she is leaving the house with her parents, she locks her four-year-old brother in a secret cupboard of sorts so that he doesn't have to go, and tells him that she will be back for him. (Yikes.) The other is the story of an American journalist living in Paris who learns of the Vel' d'Hiv roundup and how what she uncovers about that event changes her life and impacts her relationships. 
 I found the book to be remarkably well-paced, too, alternating chapters at the beginning of the book between the Holocaust and current day stories. This built some great dramatic tension, as each side of the story is missing the knowledge of the other. 
 I loved it. I could imagine someone getting totally cynical about it, but even though I predicted particular parts of it, I still found it to be enormously effective. I was bawling as I read the last pages. This may or may not be related to pregnancy hormones. :)