He was a methodical man.
A slight patter caught the ear of Vic, like the running of many small children over a heavy carpet, and then two shades blew around the side of the house, one small and scudding close to the ground, the other vastly larger--a man on horseback.

It seemed a naked horse at first, so close to the back did the rider lean, and before Vic could see clearly the vision burst on them all.

Several things kept shots from being fired earlier.
The first alarm had called attention to the opposite side of the house from that on which the rider appeared; then, the moon gave only a vague, treacherous light, and the black horse blended into it--the grass lightened the fall of his racing feet.
Like a ship driving through a fog they rushed into view, the black stallion, and Bart fleeting in front, and the surprise was complete.

Vic could see it work even in the sheriff, for the latter, having his rifle trained towards his right jerked it about with a short curse and blazed at the new target, again, again, and the line of the posse joined the fire.

Before the crack of their guns went from the ears of Vic, long before the echoes bellowed back from the hills, Satan leaped high up.
Perhaps that change of position saved both it and its rider.