This, Mrs. Hardy judged, was another such communication, which was why the person who delivered it had been careful to hurry away after ringing the bell.
Mr. Hardy did not return home until late that afternoon. He had been over to Barmet village where the Federal authorities were closely watching two men thought to be in league with the counterfeiters. Mr. Hardy had followed one man to a near-by city and seen the fellow pass a small package to a woman in black, who had quickly disappeared in a crowd. But the noted detective knew the woman and knew where she could be located when wanted.
The boys had arrived back from school, had left their books at the house, and had set out with Chet Morton for a cruise in the motorboat. When Mr. Hardy came back he glanced over his mail and was settling down to read the evening paper when his wife remembered the note that had been left at the door that afternoon.
"Some one left a letter for you this afternoon," she said. "I heard the doorbell ring, but when I went to answer it there was no one at the door. I picked up a letter, though, and I put it on your study table."
Fenton Hardy went into the study and picked up the letter, slitting open the envelope. Within, was a thin sheet of cheap paper on which had been written a few lines in pencil.
He read the message with a slow smile, then handed the paper over to his wife.
"Some one trying to scare me," he said.
She picked up the note. In a crude, ill-formed hand, she read the following:
"Better give up this counterfeit case or we'll take the shirt off your back. We know this game too well. Let this be a warning to you. Poor Blum is a rank outsider. Better let him go."
Mrs. Hardy looked up anxiously.