Shadow People - Forever Watching

Did you see that dark, fleeting shape out of the corner of your eye? Perhaps you caught a glimpse of a strange dark entity. What are they: dark ghosts, beings from some other time or dimension? Whatever they are, they can be terrifying to those who see them. What is their purpose? Why are they lurking in the shadows? Why are they watching and following us? Are these shadowy figures ghosts, inter-dimensional beings, time travellers or something darker and more evil?