At the Bureau by Steve Rasnic Tem

The story of a fishing permit administrator who becomes obsessed with a shadowy figure that watches him outside of his bleak, lifeless office. He becomes angry and tries to catch the figure in the hall, only to find himself staring in at the man in his office, a shadowy figure himself.

The ultimate stir-crazy short story. A haunting and methodically paced tale, about the banality of office work and the insanity it can cause.