As he tried another spot, again thunder beat the long roll on its iron drum outside, in the night. The lights blinked--wavered--recovered.

"The lights are going out again," said Dale dully, her excitement sunk into a stupefied calm.

"Let them go! The less light the better for me. The only thing to do is to go over this house room by room." He pointed to the billiard room door. "What's in there?"

"The billiard room." She was thinking hard. "Jack! Perhaps Courtleigh Fleming's nephew would know where the blue-prints are!"

He looked dubious. "It's a chance, but not a very good one," he said. "Well--" He led the way into the billiard room and began to rap at random upon its walls while Dale listened intently for any echo that might betray the presence of a hidden chamber or sliding panel.

Thus it happened that Lizzie received the first real thrill of what was to prove to her--and to others--a sensational and hideous night. For, coming into the living-room to lay a cloth for Mr. Anderson's night suppers not only did the lights blink threateningly and the thunder roll, but a series of spirit raps was certainly to be heard coming from the region of the billiard room.

"Oh, my God!" she wailed, and the next instant the lights went out, leaving her in inky darkness. With a loud shriek she bolted out of the room.

Thunder--lightning--dashing of rain on the streaming glass of the windows--the storm hallooing its hounds. Dale huddled close to her lover as they groped their way back to the living-room, cautiously, doing their best to keep from stumbling against some heavy piece of furniture whose fall would arouse the house.

"There's a candle on the table, Jack, if I can find the table." Her outstretched hands touched a familiar object. "Here it is." She fumbled for a moment. "Have you any matches?"

"Yes." He struck one--another--lit the candle--set it down on the table. In the weak glow of the little taper, whose tiny flame illuminated but a portion of the living-room, his face looked tense and strained.

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"It's pretty nearly hopeless," he said, "if all the walls are paneled like that."

As if in mockery of his words and his quest, a muffled knocking that seemed to come from the ceiling of the very room he stood in answered his despair.

"What's that?" gasped Dale.

They listened. The knocking was repeated--knock--knock--knock--knock.

"Someone else is looking for the Hidden Room!" muttered Brooks, gazing up at the ceiling intently, as if he could tear from it the secret of this new mystery by sheer strength of will.