I recently read 13 Little Blue Envelopes, and liked it so much I was glad the second book The Last Little Blue Envelope was due out within weeks.
The premise of both books is that Ginny's Aunt Peg has left her a bequest of 13 blue envelopes that will lead her on a journey around Europe if she chooses to follow the instructions in the letters. Of course the letters lead Ginny to much more than just physical travels. Once I suspended my disbelief long enough to accept that 17-year-old Ginny's parents would allow her to travel by herself with no phone or computer access, I was able to appreciate Aunt Peg's genius and creativity. At each stop on the journey Ginny is forced to be bold and strong. She sees remarkable sites that are not the usual for European tours and meets interesting people, neither of which were likely to happen if she had stayed in NJ all summer. Despite not having seen her aunt for a few years before her death, Ginny trusts her aunt's guidance and gets to know her and of course herself through the letters and the places she visits. Clearly this is what the story is all about...the journey of self-discovery.
This type of book is popular with teens because they all long for a journey that will take them closer to themselves, but few, if any, have an opportunity like Ginny's to leave family, friends, and the usual safety nets "to strive, to seek, to find, and not to yield" (Tennyson).
The second book takes place during Christmas vacation the same year, Ginny's senior year, a year of BIG decisions. She returns to England to complete the last portion of the quest. The end of Ginny's search is not surprising, but it is satisfying and reassuring.