Free The Disappearing Floor by Franklin W. Dixon

it.
    â€œTelegram for Frank and Joe Hardy,” said a messenger.
    Frank signed for it and ripped open the yellow envelope as he brought it into the living room.
    â€œHey! It’s from Dean Gibbs at Western State University!” He read the telegram aloud:
    PROFESSOR DARROW’S SISTER EAGER TO FIND HIM. IF POSSIBLE PLEASE CONTACT PROFESSOR. ASK HIM TO CALL HER.
    â€œWow! What a break!” Joe exploded.
    Chet looked puzzled. “How do you figure that?”
    â€œThis gives us a perfect excuse to go right up to the Perth mansion and find out what’s going on!” Frank explained. “Want to come along?”
    â€œWell, I dunno.” Chet squirmed uncomfortably. “Maybe you’d better count me out.”
    â€œDon’t be chicken. You’re coming with us!” Joe said, slapping the plump youth on the back.
    Frank said, “I just thought of something. If Professor Darrow taught crime-detection methods, maybe we can find some articles by him in Dad’s journals. That’ll give us material to work up a conversation with him. It might even furnish us a clue to his research project!”
    â€œGood idea!” Joe agreed enthusiastically.
    In their father’s study the Hardys checked the annual index of each of the three criminology journals to which their father subscribed. They could find only one article authored by Aden Darrow. It dealt with new data on the power of light beams.
    Although the article gave no hint of Darrow’s present field of research, it did include a photograph of the professor demonstrating some ultraviolet equipment. He wore eyeglasses and was bald, with a rumpled fringe of gray hair.
    â€œWell, at least we know what he looks like,” Joe remarked.
    The boys hurried to the Hardys’ convertible. A red glow of sunset suffused the western sky as they drove out of Bayport’s residential district and into the wooded outskirts of town. Soon they pulled up on the dirt lane directly in front of the Perth mansion.
    â€œYou fellows handle it,” Chet said. “I’ll stay in the car.”
    Grinning, Frank and Joe walked up the tree-covered slope to the house. Joe pressed the doorbell. Moments passed. He was about to ring again when the door suddenly opened. A tall, dark-haired, hatched-faced man confronted them.
    Noel Strang!
    â€œWell, what do you want?” he demanded, giving the boys a hard stare.
    â€œWe have a message for the man who lives here,” Frank said boldly.
    â€œI live here,” Strang retorted. “What is it?”
    â€œWe mean Professor Aden Darrow,” Frank said, displaying the telegram.
    Strang reached out to take it, but Frank made no effort to give him the paper. “Sorry, but the message is personal. It’s from his sister.”
    â€œToo bad!” Strang snapped. “Professor Darrow suffered a breakdown from overwork and had to leave on a long vacation. I have no idea how to reach him.”
    â€œDid he go out of the country?” Joe spoke up. “If so, maybe we could—”
    The door slammed in the boys’ faces!
    Frank and Joe looked at each other uncertainly then turned and started down the veranda steps. In the gathering dusk a light suddenly blazed on in an upstairs window. Joe glanced up over his shoulder, then clutched Frank’s arm.
    â€œLook!” he exclaimed.
    Through the window curtain, they glimpsed a man who seemed to resemble Professor Darrow! An instant later he moved out of sight.
    â€œStrang’s probably watching us,” Frank muttered. “Let’s go!”
    At the car they discussed their next move.
    â€œLet’s drive around till it gets dark, and then come back and keep watch on that window,” Joe suggested.
    â€œOkay,” Frank agreed.
    Leaving the dirt lane, the boys cruised back and forth along the main road until darkness had closed in. Then they returned and parked their convertible well out of range of