away."

"Well, that's a possibility, of course," assented his chum. "But they don't look as if they had been in prison. They're too well dressed, and they look too well fed for that. In fact they look more like Germans than Frenchmen."

"They do," assented Roger, as he peered over his friend's shoulder. "Still you can't always tell. At one time we thought Captain Dickerson looked like a German, but he wasn't. But the fact that these men are in civilian clothes is what gets me. They haven't any right so far inside our lines dressed like that."

"You're right," said Jimmy. "There's some sort of a mystery here. It may turn out all right, and it may be all wrong. I'm going to——"

Jimmy interrupted himself to utter an exclamation of surprise, for suddenly one of the men leaned over the table and blew out the candle, leaving the dugout in darkness. And, almost as if this was a signal of some sort, there began a furious bombardment, the echoes of which came to the ears of the Khaki Boys.

"They're at it again!" cried Roger.

"Those are our guns!" declared Jimmy. "We're paying the Huns back for smashing our fine dugout!"

"The one we took from the Germans," added his chum. "Say, Jimmy," he went on. "You know all this around here used to be within the German lines; this tunnel and the dugouts."

"Of course I know it," returned Jimmy. "What of it?"

"Well, maybe there's a secret passage leading over to their new lines and trenches from here. Maybe that's how those two civilians got in here."

"Nothing like that!" declared Jimmy. "The German lines are too far away from here now. Besides, why would two lone Germans venture back in the enemy's camp? It isn't reasonable."

"Well, there's something queer," declared Roger, "and we'd better report it."

"I guess so," agreed the young sergeant. "But now what shall we do—go ahead or wait here?"

"Let's show a light and go on," decided Roger, for they had darkened their flash torches on seeing the burning candle. They had stood in the darkness while looking into the dugout containing the four men.

Jimmy hesitated a moment. He did not at all like the situation. It was "extremely ticklish," he said afterward. To show a light now, when the four men were in darkness, would mean that Jimmy and Roger would be targets for any hostile act. They would be in plain view while the others were not. Roger guessed something of what was passing in Jimmy's mind for he said:

"There can't be any danger. Those were two of our own doughboys there."

"Yes," was the answer. "I guess we can take a chance. But have your automatic ready while I show the glim. No telling what may happen."

Roger let a faint gleam escape from between two fingers which he pressed over the small bulb of his pocket flash lamp. He directed this gleam into the dugout, and then he and his chum received another surprise.

For the place was empty. The four men—two soldiers and two civilians—had disappeared!

As Jimmy and Roger stood in the tunnel, a few feet away from the door leading into the dugout, from behind them came Bob's voice.

"Say!" he whispered, "are you fellows going to stand there chinning all day? We want to get Iggy somewhere so we can see what the matter with him is! What's the row, anyhow—why the traffic hold-up?"

"Something queer going on here, that's all," answered Roger. "Come on now—the way's clear. Wow! Hear that gun!"

"One of our big new ones," remarked Jimmy, as the concussion shook the tunnel and rattled down particles of dirt from the sides and roof.

"If there's fighting going on we ought to be in it!" exclaimed Franz, as he and Bob started on again with the disabled Iggy. They could see the dim gleam of Roger's lamp ahead of them.

"Oh, we'll get in it as soon as anyone," remarked Jimmy. "But first we want to find out what's going on here. Come on, fellows. We can get out of the tunnel and into this dugout, anyhow. This place seems to be all right. I know my way out. The cave-in didn't extend this far back."

This was true. The big shell that had brought their rest dugout down about the heads of the Khaki Boys had done no damage here. One end of the tunnel—that nearest the big underground shelter—was partly demolished, but the end connecting with the second dugout was not disturbed.

Into this dugout, then, went the five Khaki Boys, Iggy shuffling along by putting his arms over the shoulders of Franz and Bob. They had been obliged to proceed sideways in single file along the narrow tunnel, but the dugout was large enough to accommodate a dozen or more.

"They aren't here!" exclaimed Jimmy, as he quickly looked around the place, Roger having relighted the candle in the bottle.

"Who aren't here?" Franz demanded.

"The four men we saw when we stopped so suddenly," Jimmy explained. "They've gone!"

"Where?" Roger wanted to know.

Jimmy pointed to a rude door leading out of the tunnel. It was answer enough.

"Say, you fellows act as though there was a dark mystery here," complained Bob, as he helped Iggy to a seat on a box.

"I'm beginning to think there is," was Jimmy's answer. And hardly had the words passed his lips than from the door leading out of the dugout came a voice saying:

"Come on now! We can get 'em this way, I guess!"

The four Khaki Boys drew their revolvers and stood tense and waiting, forming a protecting screen in front of Iggy.

CHAPTER IV
RECOGNITION

Naturally, after what had happened and bearing in mind the strange sight Roger and Jimmy had witnessed, there was but one thought in the minds of at least four of the Khaki Boys—Iggy was temporarily out of it. And this thought was that some disaster had overtaken the American forces above ground while much was happening to them below ground, in the dugout and tunnel. Perhaps the Germans had made a counter-attack, retaken the trenches from which they had been driven, and were now about to swarm down into the dugout, where the Khaki Boys were, to capture them.

"Don't give up!" cried Jimmy fiercely. "Stand 'em off as long as you can, and then——"

Once more he was interrupted by a voice coming from the passage leading from the dugout.

"Lively now!" was the command. "There's a bare chance we may get 'em out this way, but we've got to hurry!"

"You won't get us out alive!" said Bob fiercely, and he looked around the dugout for some way of escape. There were only two entrances—or exits—whichever one might choose to call them—the one by which the boys had emerged from the tunnel, and the other by which they hoped to leave. But this last was now blocked by an approaching party.

"Stand together, boys!" said Sergeant Jimmy in a low voice.

"Shall I douse the glim?" asked Franz.

He was about to blow out the candle when into the dugout came hurrying a squad of khaki-clad soldiers, and it needed but a glance from the Khaki Boys to show them that they were their own comrades of the 509th Infantry. Lieutenant Morrison was in charge—an officer of whom the five Brothers were very fond.

"Here they are!" cried the lieutenant. "How in the world did you boys escape? We saw the place where the big German shell struck, and we didn't think there'd be more than half of you left alive after the dugout caved in, as it must have done. Yet here you all are."

"One's missing, sir," said a corporal.

"There were five and——"

"Here I iss!" exclaimed Iggy. "Part of me is alife, anyhow!"

There was a laugh at this—a laugh that told of overstrained nerves being mercifully relieved.

"Is he badly hurt?" asked Lieutenant Morrison, as he looked at the Polish lad, his friendly guard moving away from in front of him.

"Something fell on one foot when the dugout gave way under pressure from the Hun shell," explained Roger. "I hope it isn't bad."

"Well, we'll get him to a