The fireplace was obviously not what it seemed, there must be a space behind it unaccounted for in the building plans.

Now what was the next step detectives always took?
Oh, yes--they looked for panels; panels that moved.

And when one shoved them away there was a button or something.
She pushed and pressed and finally something did move.

It was the mantelpiece itself, false grate and all, which began to swing out into the room, revealing behind a dark, hollow cubbyhole, some six feet by six--the Hidden Room at last! "Oh, Jack, be careful!" breathed Dale as her lover took Miss Cornelia's candle and moved toward the dark hiding-place.

But her eyes had already caught the outlines of a tall iron safe in the gloom and in spite of her fears, her lips formed a wordless cry of victory.
But Jack Bailey said nothing at all.