"Part of the general mystery," said Bart. "It's too deep for me. If Frank knows it, why perhaps he'll tell."
"I wish I could," their chum answered, and the boys noticed that he was quite solemn. "It's something that concerns me personally, and I am not in a position, yet, to tell any one. I have only suspicions to go on, and it would not be fair to tell them to any one, until I see how near the truth I am. I admit I must seem to be acting strangely, but I can't help it. I wish I had caught that man. I believe he holds the secret I wish to solve. Where did you meet him?"
Bart told the circumstances connected with taking Mr. Hardman to the woods, and of his curious questions.
"Tell me over again that one he asked about sick persons finding their way through the woods," Frank asked, and Bart repeated it. Frank seemed to ponder over it.
"I think I'll try to see him at the hotel," Frank remarked a little later. "He may come back tonight. If he does, and I can get any clues to what I want, I may have something to tell you."
"I think we can give you a piece of news now," Ned put in. "We have been keeping it a secret, thinking the time would come when you could make use of it. Well that time seems to have come now."
Then he related what had taken place the night he was kidnapped by the Upside Down Club, and detailed the conversation of the two men in the vacant house.
"Are you sure about this?" asked Frank. "Are you sure they spoke about my uncle, and property and a sanitarium?"
"Positive," replied Ned. "Why?"
"It all fits in!" exclaimed Frank. "It bears out my theory. Now, if I could only find the place, I would have something to work on. Perhaps you fellows could help me!"