Grace, the crook, is acquitted after Kelly, the detective, has brought all his machinery to bear to convict her. In the dive which she inhabits she finds under the influence of opium, Nell, a society woman who is almost her double. In Nell's purse Grace finds a note telling of the costume that she (Nell) is going to wear at a fashionable masquerade that night. Grace goes to the masquerade as Nell and there meets Nell's twin sister, Jo, and Kelly, the detective. Neither suspects that she is not Nell. At the height of the ball Grace steals a pearl necklace from a society leader. The ballroom becomes a scene of confusion, and to complicate matters, Nell puts in an appearance. With the twin sisters and Grace in the same room the detective sees that he has been tricked. He is about to arrest Grace when the woman crook makes a clever escape. He traces her to the dive and comes face to face with her. Grace shows him Nell, his sweetheart, sleeping off the effect of the drug. In rapid succession Grace beats the detective three times and again escapes. The detective again locates Grace in a café. After closing every avenue of escape he goes to her and presents her with a jewel box. The woman opens it to see the present. It contains a pair of handcuffs. She is taken. The story ends when Nell promises the detective to forever forsake the drug of so many sorrows.