For how, in the name of Sanity, did the occupant of this room—­and obviously it was occupied at times—­enter and leave it?

“Ah!” he muttered, shining the light upon a row of yellow-bound volumes from which he had commenced his tour of inspection and to which that tour had now led him back, “it is uncanny—­this!”

He glanced back at the rectangular patch of light which marked the trap whereby he had entered this supernormal room.  It was situated close to one corner of the library, and, acting upon an idea which came to him (any idea was better than none) he proceeded to throw down the books occupying the corresponding position at the other end of the shelf.

A second trap was revealed, identical with that through which he had entered!

It was fastened with a neat brass bolt; and, standing upon one of the little Persian tables—­from which he removed a silver bowl of roses—­he opened this trap and looked into the lighted room beyond.  He saw an apartment almost identical with that which he himself recently had quitted; but in one particular it differed.  It was occupied...  And by A woman!

Arrayed in a gossamer nightrobe she lay in the bed, beneath the trap, her sunken face matching the silken whiteness.  Her thin arms drooped listlessly over the rails of the bunk, and upon her left hand M. Max perceived a wedding ring.  Her hair, flaxen in the electric light, was spread about in wildest disorder upon the pillow, and a breath of fetid air assailed his nostrils as he pressed his face close to the gauze masking the opening in order to peer closely at this victim of the catacombs.

He watched the silken covering of her bosom, intently, but failed to detect the slightest movement.

“Morbleu!” he muttered, “is she dead?”

He rent the gauze with a sweep of his left hand, and standing upon the bottom shelf of the case, craned forward into the room, looking all about him.  A purple shaded lamp burnt above the bed as in the adjoining apartment which he himself had occupied.  There were dainty feminine trifles littered in the big armchair, and a motor-coat hung upon the hook of the bathroom door.  A small cabin-trunk in one corner of the room bore the initials:  “M.  L.”

Max dropped back into the incredible library with a stifled gasp.

“Pardieu!” he said.  “It is Mrs. Leroux that I have found!”

A moment he stood looking from trap to trap; then turned and surveyed again the impassable walls, the rows of works, few of which were European, some of them bound in vellum, some in pigskin, and one row of huge volumes, ten in number, on the bottom shelf, in crocodile hide.

“It is weird, this!” he muttered, “nightmare!”—­turning the light from row to row.  “How is this lamp lighted that swings here?”

He began to search for the switch, and, even before he found it, had made up his mind that, once discovered, it would not only enable him more fully to illuminate the library, but would constitute a valuable clue.