Watson went on: 

“First, did Hobart Fenton open the Spot?  Or was it a period?  By ‘period’ I mean, did it open by chance, as it did when it caught Harry and me?  Just what did Hobart do?  Tell me!”

It was a singular question.  How could they answer it?  However, Dr. Malloy related as much as he knew of what Hobart had done; his wires and apparatus were now merely a tangled mass of fused metals.  Nothing remained intact but the blue gem and the red pebble.

“I see.  And this pebble:  you found it by digging in the cellar, I suppose.”

How did he know that?  Dr. Hansen brought that curiously heavy little stone and laid it in Watson’s hand.  The newcomer touched it with his finger, and for a brief moment he studied it.  Then he looked up.

“It’s the small one,” he stated.  “And you found it in the cellar.  It was very fortunate; the opening of the Spot was perhaps a little more than half chance.  But it was wonderfully lucky.  It let me out.  And with the help of God and our own courage we may open it again, long enough to rescue Hobart, Harry, and Dr. Holcomb.  Then—­we must break the chain—­we must destroy the revelation; we must close the Spot forever!”

Small wonder that they couldn’t understand what he meant.  Dr. Hansen thought to cut in with a practical question: 

“My dear Chick, what’s inside the Spot?  We want to know!”

But it was not Watson who answered.  It was Mme. Le Fabre.

“Spirits, of course.”

Watson gave a sudden laugh.  This time he answered: 

“My dear lady, if you know what I know, and what Dr. Holcomb has discovered, you would ask yourself a question or so.  Possibly you yourself are a spirit!”

“What!” she gasped.  “I—­a spirit!”

“Exactly.  But there is no time for questions.  Afterwards—­not now.  Five hours, and we must—­”

Someone came to the door.  It was Jerome.  At the sight of Watson he stopped, clutching the stub of his cigar between his teeth.  His grey eyes took in the other’s form from head to shoe leather.

“Back?” he inquired.  “What did you find out, Watson?  They must have fed you well over yonder!”

And Jerome pointed toward the ceiling with his thumb.  It wasn’t in his dour nature to give way to enthusiasm; this was merely his manner of welcome.  Watson smiled.

“The eats were all right, Jerome, but not all the company.  You’re just the man I want.  We have little time; none to spare for talk.  Are you in touch with Bertha Holcomb?”

The detective nodded.

Watson took the chair that Fenton had so strangely vacated and reached for paper and pencil.  Once or twice he stopped to draw a line, but mostly he was calculating.  He referred constantly to a paper he took from his pocket.  When he was through he spread his palm over what he had written.

“Jerome!”

“Yes.”