Aww ... this is a completely awesome fic. I love the Doctor being mysterious, possibly because he "isn't interesting" ;D. Also, as has been mentioned earlier, Alison's POV is amazing and really brings the reader into the fic from the viewpoint of someone discovering the relationship, and, as such, manages to showcase the dynamics of their relationship very well. :D

Also, like everyone else, I loved the mid-fic exchange between the two of them when the Master discusses being defined by the Doctor because that? Is SO. CANON. ;D