If you have read Sarah's Key, can you point to any themes that are found in both books?

The obvious similarity is that the stories are told by present day characters and how things from the past become very important to them.
Another similarity is the varying reaction of the present day characters as the secrets from the past are revealed. Some want to know and some do not. Some think it is very important to get to the truth of all the past events and some thing the pursuers of the truth are a little crazy for pursuing it. In both we are also seeing our present day characters facing serious relationship issues with family and mates and these in both stories make these characters very human to us.

Both books center around siblings who are very close despite different sexes. The older sibling in each story is protective of the younger one and both find an unexpected result of their attempt to make something special occur - protection in the cupboard and a 40th birthday celebration.