"She is still a girl, you see," smiled Paul.
Entering into the fun of the thing they allowed a full minute to elapse, and then set off to find her.
They went through the castle from roof to basement, exploring every place capable of affording concealment. But Barbara was invisible; she had vanished as if completely melted to air.
Half-an-hour had passed in this search. Then they went again through the building loudly calling her by name, and, proclaiming themselves beaten, they invited her to come forth from her hiding place.
Their appeal met with no response. They stared dubiously at one another. The affair had begun to lose its humorous side. The death-like silence, Barbara's invisibility, the gray twilight now stealing through the castle, caused it to assume a somewhat ghostly aspect.
"She must have gone outside," said Lambro.
"She promised to keep within the building," observed Paul.
For the third time they explored the castle, ending their search on the highest landing of the staircase. Here they paused before the locked door of the mysterious study.
"She is perhaps concealed here," suggested Paul.
"Impossible," returned Lambro, pointing to the wax. "The Master's seal is unbroken."