Paris, July 1942: Ten year-old Sarah is brutally arrested with her family in the Vel d'Hiv roundup, the most notorious act of French collaboration with the Nazis. But Sarah has locked her brother in their favorite hiding place and kept the key, thinking she will return soon. Paris, May 2002: On Vel d'Hiv's sixtieth anniversary, American journalist Julia Jarmond is asked to write about this black day in France's past. In the course of her investigation, Julia stumbles onto a trail of family secrets that connect her to Sarah.