The Footprints Under the Window — Franklin W. Dixon

NOTE: There are two different Hardy Boys books by this title. One was published in the early 1950's, and the other - a completely different book - was written in the 1970's. This is one of about 6 instances of this.
Although some stories were merely changed (Or 'updated'), some, including this one, were completely scrapped and the title re-used. The early versions have never been re-printed and are quite scarce, today.