Nothing seemed to happen, but I could tell by the look of intentness on his face that he was getting along all right and was not worrying.

Suddenly the look on his face changed to one of extreme satisfaction.  He dropped the disc he was holding to his ear back into its compartment and turned to me.

All at once it seemed as if the room in which we were was peopled by spirits.  There was the sound of voices, loud, clear, distinct.  It was uncanny.

“He has just come in,” remarked Craig.

“Who?” I asked.

“Lockwood—­can’t you recognize his voice?  Listen.”

I did listen intently, and the more my ears became adjusted, the more plainly I could distinguish two voices, that of a man and that of a woman.  It was indeed Lockwood and the Senorita, far above us.

I would have uttered an exclamation of amazement, but I could not miss what they were saying.

“Then you—­you believe what he says?” asked Lockwood earnestly.

“Professor Kennedy has the prints,” replied Inez tremulously.

“You saw them?”

“Yes.”

“And you believe what he says, too?”

There was a silence.

“What is it?” I asked, tapping the box lightly.

“A vocaphone,” replied Kennedy.  “The little box that hears and talks.”

“Can they hear us?” I asked, in an awestruck whisper.

“Not unless I want them to hear,” he replied, indicating a switch.  “You remember, of course, the various mechanical and electrical ears, such as the detectaphone, which we have used for eavesdropping in other cases?”

I nodded.

“Well, this is a new application which has been made of the detectaphone.  When I was using that disc from the compartment there, I had really a detectaphone.  But this is even better.  You see how neat it all is?  This is the detective service, and more.  We can ‘listen in’ and we don’t have to use ear-pieces, either, for this is a regular loud-speaking telephone—­it talks right out in meeting.  Those square holes with the converging sides act as a sort of megaphone to the receivers, those little circles back there inside magnifying the sound and throwing it out here in the room, so that we can hear just as well as if we were up there in the room where they are talking.  Listen—­I think they are talking again.”

“I suppose you know that Whitney and I have placed detectives on the trail of Norton,” we could hear Lockwood say.

“You have?” came back the answer in a voice which for the first time sounded cold.

Lockwood must have recognized it.  He had made a mistake.  It was no sufficient answer to anything that he had done to assert that some one else had also done something.

“Inez,” he said, and we could almost hear his feet as he moved over the floor in her direction in a last desperate appeal, “can’t you trust me, when I tell you that everything is all right, that they are trying to ruin me—­with you?”