Hilda and Berta Nordstrom, although identical in appearance, are opposites in temperament. Berta weds naval engineer Robert Hallowell, deserts him in Europe, and travels to the Orient in search of the gay life where she becomes a notorious courtesan known as The Yellow Typhoon. Meanwhile, Hilda has become a secret service agent and is assigned to protect Hallowell while he perfects an invention to insure American submarines against enemy attacks. Berta, in league with saboteur Karl Lysgaard to steal the plans, raids Hallowell's bungalow and kills the engineer. However, the plans are in possession of Lieut. Commander John Mathison who is transporting them to Washington. Hilda sails aboard his ship as do Berta and Lysgaard. Mathison does not wholly trust Hilda but when she foils the plotters' final attempt to steal the plans, he becomes convinced of her sincerity. The police arrive and in the ensuing fight, Karl and Berta are slain. In Washington, Mathison and Hilda deliver the plans and declare their love for each other.