the job of filling the pit. Wagg set down the shield on its edge, as
if needing to rest for a moment.

"Open that chimney door and dodge in. Pull the door to behind you."

At the base of the chimney Vaniman beheld the iron door provided for
the convenience of cleaners and repair men. The padlock of the door was
unhooked. He lifted the door from its latch, crawled into the chimney,
and pulled the door shut. A moment later, waiting in the stifling
darkness, he heard the rattle of metal against metal and the snap of the
padlock. There was the tramp of departing feet. Gradually he became
able to see about him in some degree. Away up above him was a square of
sunlit sky at the top of the shaft. He saw in one corner a large pail
with a cover; inside it were several bottles. Also, there was a bundle
of clothing.

Judging from the amount of food, it was rather evident that Mr. Wagg
expected prison-bird Two-Seven-Nine to play chimney swallow for some
little time!

Wagg had made a quick job of locking in Vaniman. The guard tipped the
upper edge of the shield inward till it rested against the chimney. He
reached around the end of the boarding and snapped the padlock. Then he
lifted his burden and went on.

About that time a lazy man in the guardroom rolled slow gaze upon the
yard. He saw Wagg moving with the burden and watched until Wagg laid it
down flat on the ground. He opined that it was a part of the
bomb-proof shelter that Wagg proposed to build in order to watch the
hillock-smashing at close range. The other guard confirmed that opinion,
having information straight from Wagg, himself.

"When does she bust?"

"Next week, so he cal'lates!"

But Mr. Wagg, returning slowly, keeping to the side of the pit farthest
from the hillock, was at that moment down to seconds in his figuring
how long it would be before the crawling fire on a fuse would reach and
sever a cord and trip a certain trigger.

"I reckon she's about due," muttered Mr. Wagg. He stopped without easy
jumping distance of the corner of a shop and slowly lighted his pipe as
an excuse for stopping.

His reckoning was correct.

The hillock heaved. The mining had been skillfully done; the mass of
rocks and earth was hoisted from behind and slid toward the pit. There
was a tremor of the ground under the prison and its yard as if Thor
had thunked viciously with his heaviest hammer. When startled men shot
glances from the windows that were handiest for observa