Tom Swift and His House on Wheels by Victor Appleton

Together Tom Swift and Ned Newton watched the door of the garage being cautiously opened. There was something peculiar in this. In the first place, no one who had a right to swing the door would have been thus cautious about it. In the second place, no one was supposed to be in that part of the shop just now except Tom and Ned. The young inventor had given orders that he was to be left undisturbed with his financial manager to make a final inspection of his new machine.

Rightly arguing that no one who had a right to be there would try to enter in this manner, Tom Swift decided to find out who was opening the door, and in such a manner as to capture the intruder if possible. Accordingly, he made a sign to Ned to keep quiet and then began creeping toward the door in as stealthy a manner as it was being opened, which was a fraction of an inch at a time.