"Don't give him that money!" cried Frank to George. "It's bad, and if you give it to him, he'll try to cheat someone else with it."
"I'll fix you!" cried the man. But at that instant there was a rattling sound at the front door, and Harry, looking through the glass panels, saw Mr. Mack, the store owner, and two or three other men outside.
"What's the matter? What has happened? Why am I locked out of my own store?" cried Mr. Mack, rattling the knob.
"There's a cheat in here!" cried Harry, unlocking the door. "There he is!" he went on, as Mr. Mack rushed in. "That man tried to pass a bad twenty dollar bill on your boy," went on Harry.
"He did, eh?" cried Mr. Mack. "Well, I'll see about that!"
"You let me go!" exclaimed the strange man. "I haven't done anything. I wanted some butter, but I changed my mind. There isn't anything wrong in that. Give me my twenty dollar bill and I'll go!"
"Oh, no, you'll not—not until you explain," said Mr. Mack, and he caught the man by the arm. Then the man tried to break away.
"Here, help me hold him!" Mr. Mack called to some of his friends who had come in with him. "We'll see what this is all about. Who can explain?" he asked, looking at Bert, Harry and Frank, in turn.
"He can," said Bert, pointing to the former circus boy.
At this the stranger took a good look at Frank, and he seemed much worried.