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