The night turned the floor-to-ceiling window into a mirror, but there was a shadow, or a shape, glimmering in it, more or less man-sized and –shaped, but not entirely distinct.
Max blinked, and it was gone. He couldn’t tell if it had been on his side of the glass or not.
He looked around. No, he was quite alone. The clock on the microwave oven read ten-fifteen: well past sundown.
E. P. Beaumont 
Very nice! Vivid, imaginative, and creepy!
Strong sense of mood in such a short selection. Well done!
This definitely has a great sense of foreboding to it!
sometimes cannot tell which side of reality visions live. Hope you are well
Nice description of the ambiguity of something acting like one-way glass.