Great was the astonishment as the cadets made out the signal from the opposite side of the hill. At least nine-tenths of them had read the message accurately, for a knowledge of signaling, both in the Morse code and the semaphore, was required at the school. After the message was received they stood staring toward the hill, looking for some further word. When the same message had been repeated three times the colonel awoke to the fact that the signalman was not going to say anything more.
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“Mr. Walker,” he called to the best signalman that the corps had. “Get your flags and answer ‘All right.’”

Cadet Walker departed on a run to his tent, to reappear shortly with two white flags. Standing where he would surely be seen by the lone signalman, the cadet began his message. The flags on the other side of the Ridge disappeared at once as the man read their signal, and Walker stopped his rapid arm movements.

“Now, what in the world do you make of that?” Terry asked, in amazement. His question was taken up by all of the cadets and asked without any satisfactory answer. Supper was neglected while the mystery was considered, and the colonel was as much puzzled as the boys were.

When the cadets finally did sit down to supper the tables buzzed with speculative talk. Many were for going over to that hill and finding out who it could have been that signaled them. At the close of the meal the colonel rapped for order and when the tent had become quiet he spoke to them of the future plans.
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“I know as little about that signal as you do, boys,” he said, “but I believe it to be sincere. Someone who is friendly is trying to give us a warning that may stand us in good stead. It is also possible that it may be a hoax, simply designed to fool us or to draw us out of camp. That will not happen, you may be sure, but I feel that we should be ready for duty. I shall split the battalion in half, and one-half of you will patrol the Ridge while the other half remains in camp to guard it against surprise.”

There was a stirring and a ripple of genuine pleasure at the news, for all of the young men looked forward to some exciting times ahead. Each one was wishing that he would be lucky enough to be in the group that would patrol the Ridge.

“I wish to make this statement, which is also an order,” went on the colonel. “There will be no carrying of arms tonight. Some one of you might become excited and fire at the wrong time, so I expressly forbid it. It is not as though you were going out alone, but you are going out in groups and therefore a weapon, in the shape of a firearm, won’t be necessary. I trust that five or six husky young cadets will be a match for the best ghost this Ridge can send against us. It may be that we will have our supreme chance to end this ugly ghost business tonight, and if so I want no slips that will damage the prospect. I wish to see the leaders immediately after the meal.”
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When the colonel met with the leaders he specified which cadets were to go out and which ones were to stay at camp. To their joy all of the friends of Don and Jim were to patrol the Ridge. The colonel had suggested that the Ghost Patrol go in a body, so the members of that secret organization prepared to go out alone. The leaders passed from group to group, telling them where to go and how to act, signals were arranged, and the stage was set.

To the waiting cadets it seemed that evening was unusually slow in coming. No attempt was made to slip out of camp until full darkness had come, for if anyone was watching it would be a risky thing to do.

“Never saw a day last so long in my life,” grumbled Vench, digging his heel into the soft mud.

“It is just about the usual length, I guess,” smiled Don. “One thing is going to be for and against us tonight.”

“What is that?” the others asked.

“There will be just enough of a moon to make us have to be careful, and just enough to help us spot the ghost if he gets out into the open.”

Jordan emerged from his tent and stopped at the various groups to give some sort of an order. When he got to the members of the Ghost Patrol he repeated it finally.
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“When we leave the camp we are to leave by the back way, taking care to keep out of the light of the fires,” he told them. “It is possible that someone is watching the camp and our game would be spoiled if we walked out in such a way that it could be seen. In about a half hour we will be able to get going.”

“The bunch in camp will have to keep their eyes wide open,” said Douglas.

“Yes, and the colonel will be helping them do it. We have to be careful that this isn’t all some tricky plan to pull us out of camp while somebody with kindly ideas rushes in and burns the place out. The colonel has arranged this signal: three rifle shots for a recall. That will mean trouble in the camp, and if you hear it, head for camp as fast as you can go.”

Darkness finally fell and the stars appeared faintly in the summer sky as the slice of the moon cut the distant horizon. One group broke up and disappeared back of the tents and another followed. Jordan got up.

“All right, let’s go,” he announced, glancing at his watch. “Slip out of camp without a sound. Keep to the shadows.”

The group in the tent broke up at once, some of them walking down the company street for a distance of three or four tents and then slipping behind them. Once out of the glare of the several campfires they had no trouble in gaining the shelter of the trees, and after a few seconds they were all ............