"Oh, well—you can't take a reward for that."
"That isn't what I'm getting at. Do you remember how the other man grabbed the bills out of his hand and turned his back to us?"
"Sure! He said he wanted to see if they were fives or ones. But it was rather funny that he turned his back to us. I thought so at the time. Still, he offered the money to us again."
"But was it the same money?"
Joe was silent. The idea had not occurred to him before.
"Do you mean," he said at last, "that perhaps the fellow changed the bills while he had his back turned?"
"Exactly."
"But why should he do that?"
"Don't you see? Perhaps the first bills were counterfeit. Perhaps the man thought that if we took the counterfeit bills and later found out that they weren't good, we would remember where they came from and start an investigation. This is only a theory, remember; but perhaps the reason he took the bills from the man they called Dock was to change them for good bills, so that we would have no cause for suspicion."
Joe nodded reflectively.
"By gosh, Frank, there may be something to
