The spiral stair was as black as pitch, and Smith was slowly making his
way down its irregular steps, when he was suddenly conscious that
something had passed him in the darkness.  There was a faint sound, a
whiff of air, a light brushing past his elbow, but so slight that he
could scarcely be certain of it.  He stopped and listened, but the wind
was rustling among the ivy outside, and he could hear nothing else.

"Is that you, Styles?" he shouted.

There was no answer, and all was still behind him.  It must have been a
sudden gust of air, for there were crannies and cracks in the old
turret.