The Mystery of the Hidden Room is a mystery novel with detective Graydon McKelvie. Ruth Darwin, a former fiancee of Carlton Davies, was blackmailed into leaving him by the man she ultimately married, powerful banker Phillip Darwin. When Darwin is murdered and Carlton finds Ruth standing over him with a gun in her hand, she is promptly arrested and sent to prison. Carlton never lost his love for Ruth and he is convinced she is innocent of the crime, but the New York City police don't share his convictions. He decides to do his own investigating, but since his butler happens to work with famous detective Graydon McKelvie, Carlton begs for McKelvie's help, and the chase starts.