Captain Nemo has built a fantastic submarine for his mission of revenge. He has traveled over 20,000 leagues in search of Charles Denver - a man who caused the death of Princess Daaker. Seeing what he had done, Denver took the daughter to his yacht and sailed away.

When respectable Lloyd Norwood becomes infatuated with moll Goldie Lewis, he falls into a life of debasement, which results in his being accused of the murder of gangland henchman Joe the Swell. Norwood's wife Mary, convinced of her husband's innocence, determines to clear his name. Disguising herself as a vamp and infiltrating the underworld, Mary extracts a confession from the real murderer, Pussyfoot Connor, who is duped by Mary into believing that he sees the ghost of the murdered man. Later, in order to have witnesses to the story, Mary takes a midnight dinner with gang leader Jack Frost, arousing the jealousy of Connor, who enters and accuses Frost of instigating the murder. The police, alerted to the scheme, rush in and arrest the criminals.