said. "Is this your secret chamber, Hildegarde?"

"Hollow?" cried Hildegarde. "What do you mean, Bell? I know of no
hollow place there."

"Have you ever looked for one?" Bell inquired. "Search would
reveal something in there, I am pretty sure."

Thrilled with curiosity, Hildegarde came down, and the three girls
crouched together on the narrow stair, and tapped and rapped here
and there. Beyond a doubt, one panel was hollow. What could it
mean?

Bell meditated. "What is on the other side of this place?" she
asked.

"I--don't know," said Hildegarde. "Stop a moment, though! It must
be,--yes, it is! The old chimney, the great square stack, comes
near this place. Can there be any space--"

"Then it IS a secret chamber, most likely," said Bell. "I have
heard of such things. Shall we try?"

They tried eagerly, pressing here, pushing there, but for some
time in vain. At length, as Hildegarde's strong fingers pressed
hard on one spot of moulding, she felt it quiver. There was a
faint sound, like a murmur of protest; then slowly, unwillingly,
the panel moved, obedient to the insistent fingers, and slid
aside, revealing a square opening into--the blackness of darkness.