I don't normally post comments, but I had to on my favorite line:
"Oh, Remus was mostly right -- James and Sirius don't know all that much about me. I'm too quiet, I suppose, but that's all right, because I know plenty about them. All three of them."
This just screams Peter to me. Its almost got this sinister tone to it - "I know them, all three of them" - that fits with him betraying them later on. But because he hasn't betrayed them yet, its toned down with humor following this part. I loved the whole story, but I think Peter's part is my favorite because I think a lot of fandom underestimates the traitorous bastard, but that line just hit spot on, you know?