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While in San Francisco there is someone who blames the oriental community for the poisonings and sets Chinatown on fire, the diabolical Master, maneuvering his network of henchmen and using disguises and secret passages, develops an infernal plan: to plague the city aqueduct with his lethal bacteria. Thanks to the tip-off from the dying Volker, a stooge dumped by the sinister Maestro, Tex and Carson ferret out the criminal from his unsuspected hideout.