Murder and the Monalet Ruby by Vickie Britton and Loretta Jackson, (Ardis Cole Series, Book 4) from Books In Motion.com

When Ardis is sent to South Dakota to handle a bequest of pioneer and Sioux artifacts left to the University of Chicago by wealthy private collector Anthony LaMoine, she gets a load of trouble that she hadnt expected - a stolen ruby, a friends missing son, and a skeleton in the cellar! Ardis learns that Anthony had an adopted son. For reasons unknown to Ardis, his son ran away from home during his teenage years. Find the son, the housekeeper tells her, and youll find the thief. But is the son really the guilty party? And is the mysterious writer-historian Seldon Drake really the man he claims to be - or an imposter?