Soon after San Francisco businessman Simon Dayton asks for help from famous detective James Lee Wong to prevent his murder, Dayton is found dead in his office. The logical suspect is Carl Roemer, an inventor who had just threatened Dayton with a gun for stealing his formula. Because the police had been summoned after the threat, Captain Sam Street is on hand to arrest the scientist, but Wong is not convinced that Roemer is guilty. He finds thin particles of glass in Dayton's office, which lab experts tell him were originally shaped like a sphere and were made of extremely brittle Bavarian glass. Dayton's autopsy also reveals that he died from poison gas. Later Wong discovers that a duplicate he has made of the sphere shatters when certain sounds are emitted. As Street tries to build his case, his girl friend, Myra Ross, who was also Dayton's secretary, helps Wong because she is certain Roemer is innocent. When one of Dayton's partners, Christian Wilk, is also found murdered in a locked room beside the glass particles, Wong's suspicions turn to a baron and his companion, Olga, also known as the Countess Dubois. Next, Devlin, Roemer's other partner, is found murdered the same way. Because Roemer was in jail at the time, he is released and is invited by Wong to come to his home. The mystery is unfolded through a trap when Wong reveals that the glass sphere cracked at the sound of a police siren and that the sphere contained poison gas, which was to be sold to a foreign power through the agents, Olga and the Baron. Dayton's company was used to smuggle the poison out of the country. As a siren is heard in the background, Roemer jumps up and tries to flee, but Wong has used an empty sphere as a decoy. It is finally revealed that Roemer killed all of the men by planting the sphere, then much later, arranged for situations in which the police had to be summoned, thus causing the sphere to break.