Dayton (Hamilton), a chemical manufacturer who has purchased the rights to an odorless and invisible poisonous gas, seeks the help of super sleuth Mr. Wong (Karloff) when Dayton's life is threatened by the inventor of the gas (St. Polis). Before Wong can meet with Dayton, the industrialist
is found dead, a victim of the deadly gas. St. Polis is arrested for the crime, but while he is in police custody, two of Dayton's business partners are also found murdered. Mr. Wong and San Francisco police captain Street (Withers) uncover a gang of international spies who want the gas formula,
but the answer to this mystery is not as obvious as it seems. In an effort to compete...