Free Footprints Under the Window by Franklin W. Dixon

through here,” Frank whispered, checking his watch. “The plane takes off in ten minutes.”
    Frank asked the gate attendant if a Mr. Martin had yet boarded the plane. The man shook his head. “I doubt it. Nobody by that name has shown me a boarding pass. But he’d better hurry—plane’s readying for take-off.”
    The attendant agreed to nod to the Hardys if Martin appeared. Frank and Joe went to stand inconspicuously against a baggage locker nearby and watched boarding passengers file through the gate. Beyond a steel-laced glass wall, landing planes blinked like huge fireflies.
    Both boys felt tense. Would they recognize Raymond Martin? Was he an ordinary traveler, or could his name be an alias for Gomez or any of the other elusive suspects?
    Five minutes passed. The jets of the silver Brazil-bound liner screamed to life.
    â€œNo, you haven’t missed him,” the attendant assured the Hardys. “Mr. Martin’s the only passenger not aboard.”
    â€œIt looks as if he’s not going to show,” Joe concluded, disappointed.
    â€œMaybe he spotted us here,” Frank said. “Quick! Let’s pretend to leave.”
    The boys hurried off through the crowd. Joe turned his head casually. The next second he grabbed Frank’s arm. “Look!”
    A middle-aged, well-dressed man was rushing toward the Flight 54 gate, trailing a white raincoat from his arm.
    â€œWait!” he shouted. “Hold the plane!”
    The Hardys were close enough to see that the man’s face was completely unfamiliar. As the passenger darted through the gate, his coat hem caught on the end of the metal railing. The man snatched the coat free, but a large piece of lining was torn off and dropped to the floor.
    The man did not stop. He ran to the landing ramp and climbed into the jetliner. A minute later the huge craft taxied off and soon rose into the night sky. Frank and Joe stood at the gate staring in chagrin after the plane.
    â€œThat was Mr. Martin, all right,” the attendant affirmed. “Too bad you boys didn’t get a chance to visit with him.”
    Frank retrieved the piece of bright plaid lining, and the brothers walked back across the terminal. “Well, I guess I led us on a wild-goose chase,” Frank apologized.
    But as he examined the torn material, he noticed a glossy, black edge protruding from a ripped seam.
    â€œJoe, look at this!”
    Frank pulled at the edge. A small roll of celluloid fell to the floor!

CHAPTER XI
    A Secret Revealed
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    FRANK stooped and picked up the celluloid coil from the floor of the air terminal.
    â€œJoe, it’s film!”
    The Hardy boys examined the torn patch from the stranger’s raincoat. A tiny pocket, now ripped, was visible in the plaid lining.
    â€œPretty clever,” Joe murmured. “The film must have been sewn in to avoid detection.”
    â€œSomething tells me we’d better take a good look at this film,” said Frank.
    The brothers hastened to a quiet corner of the terminal. Frank unfurled the strip of small film and held it up to the overhead lighting.
    â€œWhat does it show?” Joe asked excitedly.
    â€œIt’s hard to make out.” Frank squinted up at the tiny frames. “Machinery of some sort—maybe a factory interior—wait! Jumping crickets, look at this!”
    Joe grabbed the bottom of the strip and inspected the frame near his brother’s thumb. It was an outdoor view showing a high, steel fence and two uniformed figures. Joe gasped.
    â€œThe Micro-Eye plant!”
    â€œYou bet it is—and taken from inside the fence!”
    Half-incredulous, the Hardys scrutinized the film’s other frames—close-ups of the complex and labeled diagrams.
    â€œBlueprints!” Joe whispered as Frank quickly wrapped the spool in the scrap of raincoat.
    The boys had no doubt of the importance of what they had come upon: chilling evidence of