Dayton (John Hamilton), a chemical manufacturer, receives anonymous threats on his life after his company began manufacturing a dangerous poison gas. He visits the famous Chinese detective, James Lee Wong (Boris Karloff), who promises to help him. The following day, Dayton is slain by poison gas. Soon, two of Dayton’s business partners also mysteriously die from the gas.
The mystery deepens as Wong and Capt. Street (Grant Withers) of the San Francisco police encounter a gang of international spies who desire the formula of the poison gas for a foreign goveminent. The Chinese detective discovers the gas was ingeniously enclosed in a glass bulb which shattered from vibration. Wong eventually reveals the murderer to be the inventor of the gas who suspected that the murdered men were swindling him.