The Great Airport Mystery by Franklin W. Dixon

he eased into the seat beside his pal.
    â€œLuckily your suspect reached his destination before I ran out of paper,” Biff said.
    He pointed to a house a short distance away and told Frank that Zimm was inside.
    â€œHe lives there,” said Biff. “I got out and walked past the house. His name plate is posted on the lawn.”
    Frank said that he wanted to watch the house a while. “Biff, how about your driving to the nearest store and picking up some sandwiches, milk, and ice cream for us? We may be here a long time.”
    Biff went off and Frank stationed himself behind a tree. Daylight was now completely gone. The area was quiet, and light radiation fog was beginning to drift from the trees and shrubbery. Frank folded his arms against a chill that was developing in the air. He hoped that Biff would not be too long getting back.
    Suddenly the stillness was disturbed by the sound of someone whistling. It seemed to be coming from the far side of Zimm’s house. Frank recognized the tune.
    â€œHigh Journey!”
    An eerie feeling gripped him. Was he hearing the ghost of Clint Hill?
    The young detective bent low, crossed the street, and carefully edged toward the house. The sound, he was now certain, was coming from the far side of the dwelling. Frank slowly crept to the rear and listened. The whistle was louder now. He braced himself, then broke into a fast sprint.
    As Frank rounded the corner of the house, he suddenly collided with a tall man. The force of the contact threw both of them to the ground. Dazed for a second, Frank took a deep breath, then scrambled to his feet.
    The stranger also got up. He was wearing a mask! The man turned to run, but Frank was too fast for him. He managed to catch him by the collar. As the two tumbled and rolled across the ground, the stranger swung his fist.
    Frank received a hard body blow that badly stunned him. The stranger leaped to his feet and ran. Frank made an effort to pursue him, but was too late. With consternation, he watched the masked figure vanish into the darkness.

CHAPTER IX
    Alley Escape
    MEANWHILE, Joe and Chet had followed Aaron Lieber to his apartment house. It was a small stone building with doors to the outside at both the front and rear.
    They parked the truck half a block beyond it and hurried back. Joe quickly scrutinized the premises. Then he assigned Chet to guard the rear door, while he himself would watch the front.
    â€œIf Lieber has our camera hidden in his apartment, he may sneak it out,” Joe told him, “so keep your eyes open.”
    â€œOkay,” Chet answered. “Say, this kind of work sure can give a man an appetite,” he hinted.
    Joe knew that once his chum had felt the pangs of hunger, it was hopeless to try taking his mind off food. It took little prompting to send Chet rushing off to get both of them something to eat.
    The young detective watched both the front door and the service alley of the apartment house. No one came out, and it was not long before his stout pal reappeared carrying sandwiches, cartons of chocolate milk, and fruit.
    He handed Joe an apple. “This will do for an appetizer,” he announced.
    Chet then divided the rest of the food and carried his portion down the narrow alleyway to take up his post at the rear door of the building.
    Actually, Chet found two doors there. One was located at the top of a short iron stairway and led into the first floor of the apartment house.
    The second, which obviously led to the basement, was situated directly below the other. Chet looked around and selected a vantage point in the shadow of an adjacent building.
    â€œGuess nobody can see me here,” he thought.
    As Chet began munching on his third sandwich, his eyes suddenly focused on the upper door. It was, he realized, being eased open. The figure of a man carrying a large package under his arm slowly emerged. Closing the door quietly behind him, he crept down the stairway.
    â€œThe