Last night, I was sitting at my desk preparing a draft of our findings. Over the hum of the PC, I heard something scraping. The sound was like marbles grinding together in a cloth bag. I turned around slowly and stood; the sound stopped. Holding my breath, I reached out for the light switch. I paused before I flicked it, my hand hovering. Three quick taps at the window broke the spell. I flicked the switch and caught a brief glance of a shadow behind the curtains. The shadow disappeared. I stood there for a minute, straddling the chair, my arm still stretched out to the light switch, my heart racing. I went to the window and opened the curtains.

There was nothing there, of course. Whatever had been there, whatever had cast that shadow, was long gone. I switched my computer off and went to bed. I didn't sleep for a long time.

Today, I walked around the station. Lying on the ground under my window was a thick sheet of brown cardboard. It looked old and faded. The cardboard was grey, but one side was covered in a material that would once have been a rich brown. One edge was ragged, as if it had been torn away. It looks like the cover of an old book.