Carol Scott stumbles onto two mysteries quite by accident when first, during a Mardi Gras parade, she is given the strange jade shadow stone when she is mistaken for someone else. A short time later, Carol is once again mistaken for another person, Sonia and Seenia Mercier's niece, Angela, and at Sonia's request, Carol is asked to masquerade as the niece so that Seenia's poor health will not be stressed by the mistake.

Later that night, Carol meets the Mercier sisters' lawyer, Barry DeForest, who is highly interested in the shadow stone. He tries to convince Carol to give it to him to add to his collection. Carol instinctively distrusts the man.
Carol's two mysteries become connected when she once again visits the Mercier sisters and finds that their niece Angela has arrived, but the girl is connected with the mysterious shadow stone. Is the girl an impostor? And, is DeForest is cheating the sisters out of their fortune? Carol vows to discover the truth.