"How was the safe opened?"
"It was either opened by some one who knew the combination or else by a very clever crook. It wasn't dynamited at all. I'm going up to the house in a few minutes. Mr. Applegate is to call for me."
"Can't we go along?" asked Joe eagerly.
Mr. Hardy looked at his sons with a smile.
"Well, if you are so anxious to be detectives, I suppose it is about as good a chance as any to watch a crime investigation from the inside. If Mr. Applegate doesn't object, I suppose you may come along."
In a few minutes an automobile drew up before the Hardy home. Mr. Applegate was sitting in the rear seat, resting his chin on his cane. When Mr. Hardy mentioned the boys' request he merely grunted assent, so Joe and Frank clambered into the car with their father. They were tremendously excited at the prospect of being "on the inside" in the mysterious case.
While the car bowled along over the city roads toward the Tower Mansion that was gloomily silhouetted against the sky, Mr. Hardy and Mr. Applegate discussed the robbery.
"I don't really need a detective in this case," snapped Hurd Applegate. "Don't need one at all. It's as clear as the nose on your face. I know who took the stuff. But I can't prove it."
"Whom do you suspect?" asked Fenton Hardy.
"Only one man in the world could have taken it. Robinson!"