d the ramming thud of the stick as Coquenil
wedged cloth into crannies of the logs.

"There," he panted, "that's the best we can do. _Now it's up to God!_"

For a moment it seemed as if this rough prayer had been answered. There
were no more points in the barricade that showed a glow beyond and to
Coquenil, searching along the logs in the darkness by the sense of smell,
there was no sign of smoke coming through.

"I believe we have stopped the draught," he said cheerfully; "as a final
touch I'll hang that cloak of yours over the whole thing," and, very
carefully, he tucked the white garment over the topmost logs and then at
the sides so that it covered most of the barricade.

"You understand that a fire cannot burn without air," he explained, "and it
must be air that comes in from below to replace the hot air that rises. Now
I couldn't find any openings in that large room except two little
ventilators near the ceiling, so if that fire is going to burn, it must get
air from this room."

"Where does this room get _its_ air from?" asked Alice.

Coquenil thought a moment. "It gets a lot under that iron door, and--there
must be ventilating shafts besides. Anyhow, the point is, if we have
blocked this passage between the rooms we have stopped the fire from
turning, or, anyhow, from burning enough to do us any harm. You see these
logs are quite cold. Feel them."

Alice groped forward in the darkness toward the barricade and, as she
touched the logs, her bare arm touched Coquenil's bare arm.

Suddenly a faint sound broke the stillness and the detective started
violently. He was in such a state of nervous tension that he would have
started at the rustle of a leaf.

"Hark! What is that?"

It was a low humming sound that presently grew stronger, and then sang on
steadily like a buzzing wheel.

"It's over here," said Coquenil, moving toward the door. "No, it's here!"
He turned to the right and stood still, listening. "It's under the floor!"
He bent down and listened again. "It's overhead! It's nowhere
and--everywhere! What _is_ it?"

As he moved about in perplexity it seemed to him that he felt a current of
air. He put one hand in it, then the other hand, then he turned his face to
it; there certainly was a current of air.

"Alice, come here!" he called. "Stand where I am! That's right. Now put out
your hand! Do you feel anything?"

"I feel a draught," she answered.

"There's no doubt about it," he muttered, "but-