A diamond is stolen at a houseboat party given by the district attorney. He gives the thief a chance to return it by putting an empty box on a table and turning out the lights. When the lights are turned back on the box is gone, and the district attorney has a knife in his back and is quite dead. The police and the coroner arrive. There are several attempts made on the life of the coroner. Ruth Whitman is found hiding in a grandfather-clock, holding the gem box. She claims the box was pushed int...