He applied his ear to the crevice, and heard these words: 

“This lot is rather better than the last, Jones.  We can’t be too careful, or the detectives will interfere with our business.  Some of the last lot were rather coarse.”

“I know it, sir,” answered the man addressed as Jones.

“There’s nothing the matter with this,” said the old man.  “There isn’t one person in a hundred that would suspect it was not genuine.”

Jack pricked up his ears.

Looking through the crevice, he ascertained that it was a bill that the old man had in his hand.

“They’re counterfeiters,” he said, half audibly.

Low as the tone was, it startled Dr. Robinson.

“Ha!” said he, startled, “what’s that?”

“What’s what, sir?” said Jones.

“I thought I heard some one speaking.”

“I didn’t hear nothing, sir.”

“Did you hear nothing, Ferguson?”

“No, sir.”

“I suppose I was deceived, then,” said the old man.

“How many bills have you there?” he resumed.

“Seventy-nine, sir.”

“That’s a very good day’s work,” said the old man, in a tone of satisfaction.  “It’s a paying business.”

“It pays you, sir,” said Jones, grumbling.

“And it shall pay you, too, my man, never fear!”

Jack had made a great discovery.  He understood now the connection between Mrs. Hardwick and the old man whom he now knew not to be a physician.  He was at the head of a gang of counterfeiters, and she was engaged in putting the false money into circulation.

He softly ascended the staircase, and re-entered the room he left, closing the secret door behind him.

CHAPTER XXIX

JACK IS DETECTED

In the course of the afternoon, Jack made another visit to the foot of the staircase.  He saw through the crevice the same two men at work, but the old man was not with them.  Ascertaining this, he ought, in prudence, immediately to have retraced his steps, but he remained on watch for twenty minutes.  When he did return he was startled by finding the old man seated, and waiting for him.  There was a menacing expression on his face.

“Where have you been?” he demanded, abruptly.

“Downstairs,” answered Jack.

“Ha!  What did you see?”

“I may as well own up,” thought Jack.  “Through a crack I saw some men at work in a basement room,” he replied.

“Do you know what they were doing?”

“Counterfeiting, I should think.”

“Well, is there anything wrong in that?”

“I suppose you wouldn’t want to be found out,” he answered.

“I didn’t mean to have you make this discovery.  Now there’s only one thing to be done.”

“What’s that?”

“You have become possessed of an important—­I may say, a dangerous secret.  You have us in your power.”