Mary's lot. always hard, becomes doubly so upon her father's death. Desiring to re-marry, the girl's stepmother conspires to get her out of the way. Aided by Downs, the man she intends to wed, Mrs. Halleck succeeds in having Mary sent to the reformatory. Rose Hayden, a girl of the slums, dominates the inmates of the institution. Angered by punishment, Rose sets fire to the building. Due to Mary's heroism, not a life is lost. The girl informs the authorities of Rose's crime. Rose is seized, but vows revenge. Marys heroic work results in her release. The girl later secures a position as governess to Helen, granddaughter of wealthy Mrs Clark. Burton, Mrs. Clark's young brother, falls in love with Mary. Because of her past, the girl refuses to marry him. Several months later Rose escapes from the institution. The girl learns of Mary's whereabouts and blackmails her under threat of revealing her past to Mrs. Clark. When her victim's money is gone, Rose treacherously informs Mrs. Clark that she is harboring a girl who has served time. Incidentally Rose manages to steal a letter addressed to Mary, while conversing with Mrs. Clark. Horrified, Mrs. Clark orders Mary to leave the house. Burton enters and hears Rose's story. So great is his love that the boy declares he will marry Mary in spite of her past. He contemptuously orders Rose from the house. In departing the girl drops the letter she has stolen. It proves to be Mrs. Halleck's dying statement, and shows Mary to have been innocent of wrong. A commotion outside attracts the attention of Mary, her sweetheart and Mrs. Clark. They see Rose in the grasp of two detectives who have been searching for her. Thus the girl of the slums passes out of Mary's life forever.