“The wall is purely a matter of mechanical construction, operated hydraulically.”  The man was speaking softly at Jimmie Dale’s side.  “The room beneath is built to correspond; the base, ceiling, and wall mouldings here do not have to be very ingenious to effect a disguise.  I might say, however, that few visitors, other than yourself, have ever seen anything here but a bedroom.”  He waved his hand toward the retorts, the racks of test tubes, the hundred and one articles that strewed the laboratory bench.  “As for this, its purpose is twofold.  We, as well, as the police, have often need of analysis.  We make it.  If we require a drug, a poison, say, we compound it from its various ingredients, or, as the case may be, distil it, perhaps—­it is, you will agree, somewhat more difficult to trace to its source if procured that way.  And speaking of poisons”—­he stepped forward, and lifted a glass-stoppered bottle containing a colourless liquid from a shelf—­“in a modest way we have even done some original research work here.  This, for instance, is as Utopian from our standpoint as the formation, and personnel of the organisation I have briefly outlined to you.  It possesses very essential qualities.  It is almost instantaneous in its action, requires a very small quantity, and defies detection even by autopsy.”  He uncorked the bottle, and dipped in a long glass rod.  “Will you watch the experiment?” he invited, with a sort of ghastly pleasantry.  “I do not want you to accept anything on trust.”

With a start, Jimmie Dale swung around.  He had heard no sound, but another man was at his elbow now—­and, struggling in the man’s hand, was a little white rabbit.

It was over in an instant.  A single drop in the rabbit’s mouth, and the animal had stiffened out, a lifeless thing.

“It is quite as effective on the human organism,” continued the other, “only, instead of one drop, three are required.  If I make it ten”—­he was carefully measuring the liquid into two wineglasses—­“it is only that even you may be satisfied that the quantity is fatal.”  He filled up the glasses with what was apparently wine of some description, which he poured from a decanter, and held out the glasses in front of him.

And again Jimmie Dale started, again he had heard no one enter, and yet two men had stepped forward from behind him and had taken the glasses from their leader’s hands.  He glanced around him, counting quickly—­they were surely the two who had entered with him from the corridor.  No!  Including the leader, there were now six men, all in evening dress, all masked, in the room with him.

A wave of the leader’s hand, and the two men holding the glasses left the room.  The man turned to Jimmie Dale again.

“Shall we proceed to the second room, Mr. Dale?” he asked politely.  “I think it is now prepared for us—­I do not wish to bore you with a repetition of magical sliding walls.”

There was something now that numbed the ache in Jimmie Dale’s brain—­a sense of some deadly, remorseless thing that seemed to be constantly creeping closer to him, clutching at him—­to smother him, to choke him.  There was something absolutely fiendish, terrifying, in the veneer of culture around him.