There was a sound of swiftly retreating feet, a clatter on the stairs, a scramble, a shout of pain or fear, and a sudden blow.

"Quick, fellows!" cried Jack, excitedly. "Prince has found an eavesdropper!"

They rushed out, they sprang down the stairs, and at the foot they found the dog, apparently in a dazed condition, but with a piece of cloth in his mouth.

"Good dog!" cried Jack. "Where is he?"

Prince growled and chewed away at the piece of cloth.

"He got away," said Frank. "He must have struck Prince with a heavy cane, or a club, for we heard the blow. The dog was stunned, but he held fast to this piece of the fellow's trousers."

"After him!" spluttered Rattleton. "He may not be able to get away! We'll try to capture him!"

But the effort was vain. The eavesdropper had made good his escape.

After a little time the boys all came back to Diamond's room. They found Jack examining the piece of cloth, which he had taken from the bulldog with no small difficulty.