The watchful eyes.

At first glance, this is obviously a very innovative sketch with brilliant shading effects.
I am curious as to what pencil you have used for it. The shading is indeed not only detailed but fine grained and gradual. The face on the right seems more feminine and the one on the left seems more masculine so I just assumed it is a woman and a man respectively. The woman's cheek bones are very high and her eyebrows are elevated in a curious fashion. The man's features seem more consistent. The mans eyes suit the title more than the woman because they are wider, and hence more curious and watchful. If the woman's eyes were wider, they would in turn look more curious and watchful.
OVERALL: It is a brilliant sketch and so are all of your other works.