13 Little Blue Envelopes

13 Little Blue Envelopes by Maureen Johnson
13 Little Blue Envelopes is about a girl named Ginny who receives a mysterious package from her aunt, her dead aunt.  Inside the package are 13 little blue envelopes and instructions that tell her to NOT open the envelopes, to use the money provided in the package to purchase a plane ticket to London and to follow the rest of the instructions when she's there.  Ginny, since she loved and trusted her aunt, decides to do what the letter says and before long, she is on her way to Europe.  Her aunt's letters lead her in a crazy trail across Europe involving art galleries, stroopwaffle (a type of pastry), biking, a cafe with pictures of dogs painted on the walls, and of course, the mystery surrounding the 13 little blue envelopes.