Mr Secret

Year two or three.

We had a conference room on my floor in the big office building. The room was situated between two long parallell corridors and had walls of glass against both corridors.

One night that I worked a bit overtime I walked in one of the corridors. A flimsy curtain almost covered the glass wall. When I came along one of the walls of glass I saw this man doing something with something inside the conference room. He was standing on a chair and that something was situated above the curtain. At the precis point of me passing the glass wall this man twitched and ran. 

A few seconds later I arrived at the point where the door leading into the conference room is. No one was to be seen or heard. What was this man doing? Why was he running? Why did I not recognize him as one on my coworkers?