Carolyn Wells 
Clue 

An heiress has been murdered, and only Fleming Stone can see the vital evidence. Madeleine Van Norman is the most eligible young woman in the state, a beautiful young lady who is soon to come into her fortune. From her countless suitors, she makes a peculiar choice, agreeing to marry a stuffy man who loves someone else. On the eve of the wedding, Madeleine shuts herself away in a locked room to think about what she is about to do-and in the morning, she is found gruesomely murdered. Every member of the household is a suspect, but no one understands how the killer could have slipped through the locked doors of Madeleine’s bedroom. As the town whirls into a tailspin of suspicion and fear, it falls to the brilliant detective Fleming Stone to pick out the person who stabbed Madeleine to death-a baffling mystery that hinges on the discovery of a single, all-important clue. (goodreads)