Ralestone Luck is the story of an old family struck by hard times. Rupert and his younger siblings Richanda and Valerius have returned to the ancestral estate in Louisiana after losing what they held of liquid family fortune. They believe that there may be a hidden treasure on the estate that can make them solvent. They also more or less believe that the missing ancestral sword, the Luck, will restore their fortune -- if they can find it. When their possession of the estate is called into question by someone claiming to be from a lost branch of the family, they and their friendly neighbors put their heads together to find out all they can about the secrets of the estate and the man laying claim to it.
Ralestone Luck was written in 1938 and rather shows its age. It's set in Louisiana and was contemporary with the writing date. The Ralestones had originally emigrated from England and have not relinquished the title. It's a harmless, okay, slightly spooky adventure at the middle school level, but I wonder if it would be acceptable in today's social climate. I'd more strongly recommend Andre Norton's excellent science fiction and historical adventure stories; they have held up much better.
