Thirteen-year-old Sal heads out in search of her mother, and she learns how to live without her along the way. In this sense, you might say she grows up, because she's learning how to handle the tougher stuff of life, and by the end of her journey, she's a new, stronger, wiser person. In literature, we like to call this a coming of age story.
Plus, she totally succeeds on her quest. Although she struggles for a long time with admitting that she can't actually bring her mother back, Sal finally comes to terms with that fact, and bids her mother farewell. We think Sal has a lot to be proud of.
Oh, and as for that whole mystery thing? Well, Sal helps solve the mystery of her friend Phoebe's missing mother, which, as it turns out, is no mystery at all. And, of course, there's the mystery – for the readers, at least – of what happened to Sal's own mother. In any case, this book is full of secrets, and we spend a lot of our own reading time putting together the clues.