An ambitious woman doesn't care who she hurts in her drive to make her sister a star.

When the police question a woman they have pulled from a river after a suicide attempt, she admits that her name is Helen Chernen, but does not explain why she wants to kill herself. As she lays dying, however, she recalls the events that led her from the industrial town of Greenhill to this desperate moment: After their mother dies, Helen rears her younger sister, Katherine Blaine. When Helen's husband Sam refuses to buy Katie a special dress for her high school graduation, Helen vows to give her sister a better life. One evening, Katie attends a vaudeville performance with Johnny Gilpin and is enthralled by the performance of song-and-dance team Paul Collins and Albert Runkel. Later, at a soda fountain, Katie announces her intention to become an actress and does an imitation of Collins and Runkel. Unknown to Katie, Paul and Albert enter the soda fountain and see her performance. Albert is charmed by Katie and invites her to dance on the theater stage. When Albert drops Katie at home late that night, an irate Helen orders him to leave her sister alone. Later, however, Helen changes her mind and encourages Albert's interest, and shortly, he marries Katie. When Katie, Albert and Paul leave town, Helen goes with them. Helen works unceasingly to increase Katie's part in the act and eventually forces Paul to leave. After a while, Katie is offered a part in a revue without Albert. At first she refuses to go without him, but finally accepts at his insistence. Paul tells Helen that he has developed a kind of admiration for her cold ambition and then makes a pass, but when she responds, he dismisses her. Albert and Paul now resume their old act and Katie moves from the chorus to a starring role in the revue thanks to Helen's manipulation. On opening night, Katie is such a success that famous playwright Laura Bithorn resolves to write a play for her. When Albert calls to congratulate her, Helen forces her to hang up. Paul then advises Albert to go to New York immediately, but when Albert arrives at a party in Katie's honor and begs her to return to him, she quarrels with him, and he leaves despondent. While Katie becomes more famous, Albert's act fails. After a theater owner suggests that Albert capitalize on his relationship to Katie, he kills himself. Albert's death affects Katie on a deep level, and she starts drinking heavily, until finally, her producer decides to find another actress for Laura's play. Determined not to let this happen, Helen decides to produce the play herself. She and Katie join Laura for drinks and encounter Paul in the bar. While Helen discusses business with Laura, Katie joins Paul, who is now leading a popular band. Later, Katie visits Paul at the resort where he is working. They spend the next three weeks together, and Paul proposes marriage. Helen arrives at the resort, unaware that Paul is also there, and when she learns that they plan to get married, she is deeply unhappy. She points out that she has invested all her money in the play, and even though Paul insists that Katie break away from Helen before she is destroyed, Katie refuses to walk out on her sister, and Paul breaks their engagement. On opening night, Paul comes to see Katie, but Helen sends him away. When Katie learns this, she runs after him, but cannot find him. She then accuses Helen of wanting Paul for herself, and is so upset that she breaks down on stage. Later, she tells Helen that she never wants to see her again and rejoins Paul. Helen is left totally alone and broke. Back at the river, Helen dies without answering the policeman's question.