A beam of light had appeared on the loftiest spur, standing out at first like a red star in the darkness, then growing intensely brighter, and burning with a steady, vivid light.  The effect was weird and powerful.  The mountain beneath it was invisible, and it seemed to burn there like a real eye, wrathful and menacing.  The older men, as well as the boys, were held as if by a spell.  It was something monstrous and eastern, like the appearance of a genie out of the Arabian Nights.

The light, after remaining fixed for at least a minute, began to move slowly from side to side and then faster.

“A signal!” exclaimed Colonel Newcomb.  “Beyond a doubt it is the Southerners.  Whatever they’re saying they’re saying it to somebody.  Look toward the south!”

“Ah, there they are answering!” exclaimed Major Hertford.

All had wheeled simultaneously, and on another high spur a mile to the south a second red light as vivid and intense as the first was flashing back and forth.  It, too, the mountain below invisible, seemed to swing in the heavens.  Dick, standing there in the darkness and rain, and knowing that imminent and mortal danger was on either side, felt a frightful chill creeping slowly down his spine.  It is a terrible thing to feel through some superior sense that an invisible foe is approaching, and not be able to know by any kind of striving whence he came.

The lights flashed alternately, and presently both dropped from the sky, seeming to Dick to leave blacker spots on the darkness in their place.  Then only the heavy night and the rain encompassed them.

“What do you think it is?” asked Colonel Newcomb of Major Hertford.

“Southern troops beyond a doubt.  It is equally certain that they were warned in some manner from Washington of our departure.”

“I think so, too.  It is probable that they saw the light and have been signalling their knowledge to each other.  It seems likely to me that they will wait at the far end of the valley to cut us off.  What force do you think it is?”

“Perhaps a cavalry detachment that has ridden hurriedly to intercept us.  I would say at a guess that it is Turner Ashby and his men.  A skillful and dangerous foe, as you know.”

Already the fame of this daring Confederate horseman was spreading over Virginia and Maryland.

“If we are right in our guess,” said Major Hertford, “they will dismount, lead their horses along the mountain side, and shut down the trap upon us.  Doubtless they are in superior force, and know the country much better than we do.  If they get ahead of us and have a little time to do it in they will certainly tear up the tracks.”

“I think you are right in all respects,” said Colonel Newcomb.  “But it is obvious that we must not give them time to destroy the road ahead of us.  As for the rest, I wonder.”

He pulled uneasily at his short beard, and then he caught sight of Sergeant Whitley standing silently, arms folded, by the side of the engine.  Newcomb, the miner colonel, was a man of big and open mind.  A successful business man, he had the qualities which made him a good general by the time the war was in its third year.  He knew Whitley and he knew, too, that he was an old army regular, bristling with experience and shrewdness.