Free The Secret of the Old Mill by Franklin W. Dixon

didn’t want to alarm Mother and Aunt Gertrude,” Frank said, “so we didn’t tell them about the attack.”
    Mr. Hardy looked grim and warned his sons gravely to be extra cautious.
    â€œThere’s one bright spot,” he added. “The print you found on that finger guard. It could be a big break.”
    During lunch the detective was unusually preoccupied. The boys tried to draw him out by questions and deductions about the counterfeiting case. He would say very little, however, and seemed to be concentrating on a knotty problem.
    A little later the boys rode their motorcycles straight to the boathouse and parked at the street end of the jetty. “Chet ought to show up soon,” Joe remarked.
    As the brothers walked toward the boathouse Frank commented on his father’s preoccupation during luncheon.
    â€œI have a hunch Dad’s assignment is even tougher than usual,” he confided. “I wish we could help him on it.”
    Frank seemed to be only half listening and nodded absently.
    â€œWhat’s the matter with you?” Joe laughed. “I’m talking to myself!”
    Suddenly Frank stopped. He grasped his brother’s arm firmly.
    â€œJoe!” he said. “We may have found a clue in Bridgeport this morning, and didn’t realize it!”

CHAPTER X
    The Sign of the Arrow
    â€œWHAT clue do you mean, Frank?” Joe demanded eagerly.
    â€œElekton’s name was on that list Mr. Evans showed us this morning.”
    â€œYes, I know. But Dad didn’t seem excited over that.”
    â€œWell, I am,” Frank said. “Put two and two together. Every time we’ve been near the Elekton area, something has happened. First, the warning on the arrow, then the attack last night.”
    â€œOf course!” Joe said. “I get you! Someone who has access to the company’s paper supply could have sent the warnings, and knocked us out. But who? An employee of Elekton?”
    â€œThat’s the mystery,” said Frank. “Is the person trying to get at Dad through us? And which of the cases is this mysterious person connected with —the counterfeit case or Dad’s secret one?”
    â€œThen there’s the bike,” Joe recalled. “Someone from the company easily could have taken it from the storage area under the mill at night when the guard and maintenance man were inside the gatehouse.”
    â€œJoe,” said Frank slowly, “we’re theorizing on the case having a connection with Elekton. Do you think Dad is, too, even though he didn’t tell us? The Elekton name may have been the clue he found at Quality Paper!”
    Joe snapped his fingers. “My guess is that Dad is doing some detective work for Elekton! That would explain why he can’t say anything. Elekton is doing top-secret space missile work.”
    â€œIt’s possible,” Frank speculated, “that Elekton retained Dad because of the chain of sabotage acts in plants handling similar jobs for the government.”
    â€œSounds logical,” Joe agreed. “I guess Dad’s main assignment would be to ward off sabotage at Elekton. No wonder he is so anxious to find out who sent the warnings.”
    Just then Chet arrived in the Queen and leaped out.
    â€œI have a job!” he announced to Frank and Joe. Then he looked a bit sheepish. “It’s—er—in the cafeteria, serving behind the food counter. The cafeteria is run on a concession basis, and the people working there aren’t as carefully screened as the plant employees.”
    Joe grinned. “It’s not very scientific, but think of the food! You’ll be able to eat anything you want.”
    Chet sighed, and did not respond with one of his usual humorous comebacks. A worried expression spread over his face. He shifted from one foot to the other.
    â€œWhat’s on your mind?” Joe prodded. “Not nervous about the job, are