Nor the Raymond, nor the Katerina, so it is obvious that some other is N-13. The Question is, is Masha Rostova is N-13?
It doesn’t seem to be either a spoiler for the observant audience.
The Russian friend of Raymond Stepanov is already shown reluctance to identify the identity of N-13 and while we see him whisphering into ear of Raymond, it is easy to guess that Masha is the real N-13, which she is not aware of till now.
Masha a secretive and sedative past. She a memory recall/rewrite (I don’t know how to descrive) problem. So, there is a story hidden beneath the past (what is in that doll by tha way? any thumbdrive hidden?).
So, our theory suggest, Masha Rostova aka Agent Keen is N-13. with a horde of information somewhere in her mind, hidden by some clog which can be removed only by some expert memorygrapher (I just termed it) or psychologist with a doctorate in meta physics. 🙂