Who is Margo Roth Spiegelman? This is the question that's been holding Quentin's attention for as long as he's known her. For a while there - before dead men in parks and middle school spoiled everything - they were best friends. Tonight, however, she once again needs Q's help in an ultimate revenge plan against everyone who's wronged her. This is the lead-in to the mysterious quest into the disappearance of Margo Roth Spiegelman. 
 After Margo's disappearance act (was it all an act?) Q is convinced she's left clues for him and he sets out to discover who she really was/is. The search for Margo, however, leads to a search for himself as Margo's last name, Spiegelman ('Spiegel' means mirror in German and Dutch), seems to suggest: Margo is Q's mirror. When Q looks at her, what's reflected to him is not only what he wants to see in Margo, but also everything he wants to be himself. 
 Ever since the two found a dead guy in the park, Margo's been gone to him. If she had been mysterious to him before, after this clearly traumatic event, he turned her into an almost Platonic idea: there was the real Margo, and then there was his idea of Margo as the inventive, creative, enigmatic dare-all, someone, or rather something he considered to be absolute reality. As such, Margo becomes the archetypal unattainable woman or literally the girl next door. Anything "real" Margo will end up to be, can only be a disappointment. 
 Quentin starts with the Platonic idea of Margo. But the more he discovers about her through the clues she left, the less he seems to have known her and the more Q realizes that Margo wasn't the person he thought she was. The real Margo is like the map with the pins: depending on where you put the pins you get a different route to get to Margo, and maybe you even get a different destination, you get a different Margo. "How do you pinpoint a point a spot on the map when the spot seems to be moving from metropolis to metropolis." (p. 230) Now the 'idea' of Margo is no longer reflected in the 'real' Margo: the idea of Margo has become a fluid, ever-changing idea. 
 The idea of the mirror has been a constant theme throughout John Green's oeuvre. Just like musicians often make the same one song over and over again and nobody seems to care because it's a great song; just like directors often make the same movie over and over again and critics praise this because they are true to their eccentricities; so John Green has been accused of 'repeating himself' in his works. On the outset, this is what's going on. In essence, the character of Q = the character of Miles in Looking for Alaska = the character of Colin in An Abundance of Katherines. In essence Margo = Alaska = Katherine. I don't feel however this is John Green merely repeating himself. I see this as a way for John Green to explore the major theme running through his oeuvre: "looking at people", looking from the inside out and looking from the outside in. How does perspective, or 'the look' change the person you're looking at. In the beginning of Paper Towns Q looks ( or gazes - in Lacan's terms) into Margo as a mirror, and he appears to see her and by consequence himself as an ideal. By seeing himself reflected in his mirror, Margo, he can enter the world (don't forget this is all right before high school graduation) by establishing himself through the fantasy image in the mirror, an image that he would like to become later on in life. But of course, we see that towards the end of the book he ceases to see Margo as a mirror. Instead "she was a girl" (p. 199), which partly explains his final decision not to join Margo. 
 One of the strongest images in the book for me is when Quentin picks up his friend Ben from the prom party. Quentin's been too preoccupied with the search for Margo that now, this party: "It all seemed so trivial, so embarrassing. It all seemed like paper kids having their paper fun." (p. 178) He just can't bring himself to join in. He "felt so detached from all this shit, all this high-school-is-ending-so-we-have-to-reveal-that-deep-down-we-all-love-everybody bullshit. And [he] imagined her at this party, or thousands like this one. The life drawn out of her eyes. I imagined her listening to Chuck Parson babble at her and thinking about ways out, about the living ways out and the dead ways out. I could imagine the two paths with equal clarity." (p.182) Here the idea of the mirror itself falls short. It's not that Q looks at this and sees something of himself (or Margo) reflected back to him, no. Here it's like being on one side an immense glass window, looking into the world of the others. You find yourself trapped on the outside. Not only don't you know how you can find the door and how you can get on the inside, you're not really sure whether you really want to get on the inside. When Quentin comes to the realization that Margo was just a person (though no one ever thought of her as one), he realizes she also felt this "unscaleable wall surrounding her" (p.199). Margo may have started off as a mirror, but at the end of the book she's a window for Q: one through which he can finally start to accept other people's and his own flaws and imperfections. 
 There are so many more great ideas in this book. I love how John Green makes a lot of the things quite explicit, but at the same time he leaves so much for the reader to explore. There is for instance the fact that Margo left Whitman's Leaves of Grass, with certain highlighted passages, behind. As a reader you just have to be at least a little bit tempted to read this work as well. Then I haven't even hinted at the whole concept of the paper towns and the pseudovisions, the metaphor of the strings, etc. 
 Identity, personality, self-discovery... these are all key in what makes a good YA novel. With the use of some carefully chosen symbols, themes and references throughout his (still quite small) oeuvre, John Green is for me similar to someone like Paul Auster, another one of those authors who seemingly writes the same book over and over again... Well, all I want to say is: keep 'em coming, John Green!