The Tower Treasure by Franklin W. Dixon
I'm sorely tempted to revisit other 'Hardy Boys' and 'Nancy Drew' titles now, but I'll probably let the impulse pass. The Hardy Boys, two clean-cut young fellows named Frank and Joe, are nearly run down on their motorcycles one afternoon. It comes out later that there was a robbery at the prominent Tower Mansion! The family, an aging bachelor and his worst-dressed sister issue a reward for the return of the stolen jewels but are pretty unwilling to trust two teens to search their house. Nonetheless, with a father of a chum wrongfully accused of the theft, and some advice from their P.I. Pop, the Hardy Boys set out to solve the mystery.
I read the more commonly available revised version of 'The Tower Treasure', but I read up on the changes that had been made in the late 1950s to make the story more accessible to young readers and to mollify those parents who might object to a healthy dose of 1920s racism. This series, along with 'Nancy Drew', underwent some radical changes to bring their characters in line with the principles, for better or for worse, of the day.
Frankly, the history of the changes made to the series and the contractually anonymous writers who made it happen, were more interesting than the story itself. There is some clever sleuthing and red herrings along the way, but its hard to read these stories with the same enthusiasm I did as a kid.
I read revised edition of the first Nancy Drew mystery, 'The Secret of the Old Clock', at the same time and had similar feelings.