“If we ever lay our hands on the man who stole Chet’s roadster I’m sure we’ll have gone a long way toward solving the Tower affair,” said Frank to his brother. “I may be wrong, but I have an idea that the fellow was a professional crook who first set out to rob the steamboat office. Then, when he was frightened off, he hung around the city and waited his chance to rob Tower Mansion.”

Mr. Hardy was still in the library when the boys returned home. The great detective was frankly surprised when his sons again entered the room, and he looked up with the suspicion of a twinkle in his eyes.

“What! More clues!” he exclaimed. “Surely not so soon.”

“You bet we have more clues!” exclaimed Frank eagerly. “And real clues this time. We’re going to turn them over to you.”

“But I thought the two of you were working on this case in your own way. Remember, I’m the opposition.”