“Steady, boys!  Steady!” panted the officer, between his vigorous blows.  “A few more strokes and I’ll have this beam cut.  Then I think you can get out.”

Again and again he swung the keen axe.  Between the blows the boys could hear the sounds of distant firing, and the reverberation told them that heavy guns were being used.

“Hope they don’t send any more shells over this way,” murmured Bob.

“They seem satisfied, now that they have brought down the old mill on top of us,” commented Franz.  “Can any of you see the German lines!”

None of them could, it developed.  In fact, their vision was obstructed by a small hill directly in front of the grill work of their prison, and, even if this had been removed, the smoke was now swirling around them so thickly that, at times, even the officer chopping them out was obscured.

Once or twice the chopper had to stoop down, in order to breathe the purer and cooler air near the ground, and the boys were put to the same expedient.

And then, suddenly, there came a crashing, splintering sound.  There was an exclamation from the officer, and, as he leaped back he cried: 

“There she goes, boys!  The way is as clear as I can make it!  Come on out, and lively, too!”

The Khaki Boys lost no time in obeying.  Leaping and scrambling as best they could over the heaps of brick, stone and splintered wood, they emerged through the hole cut for them by the officer.  He had chopped through the one beam that held all the others, or most of the others in place, and the crisscross structure had collapsed, allowing the boys to escape.

“Come on!  Come on!” cried Jimmy.  “Everybody out!”

And they leaped out only just in time, for as Bob, the last to make his way to safety, cleared the jagged barrier, a burst of flames and smoke swept into what had been the boys’ prison.

Now they stood on the green grass, in the open, with the burning ruins of the mill at their backs.  And confronting them, still holding the axe, and panting from his terrific exertions, was the strange officer.

And as the young soldiers looked at him they wondered, more than ever, who he was.

CHAPTER XIII

A PERILOUS JOURNEY

Almost at once there set in a reaction, as was natural under the circumstances.  The Khaki Boys had been keyed up to such a high pitch through the battle, the attack on the hill, the subsequent shelling of it, and their own dangerous position after the collapse of the building, that now their rescue hardly seemed real.

“Say, I’m about all in!” exclaimed Bob, as he sank down on the grass.

“Same here,” agreed Jimmy, staggering to a seat.

“Take it easy, boys, take it easy,” counseled their rescuer.  “And better come a bit farther away from the fire.  The whole place is going, and the wind’s blowing strongly this way.  We’re too much in line with it.”