The Little Intruder (1919)

Jealous of the attention his wife Virginia receives at a seaside resort and desiring to know how far her flirtation with Henry Harding has gone, George Conklin returns to New York to hire a detective. He finds a pretty girl in his house and the police identify her as criminal Philadelphia Mary but George tells them that she is his niece that he was expecting; when the police are gone, George learns that her name is Betty McCarthy and makes her agree to spy on Virginia.