Mrs. Mooney's daughter, Polly, is well known as a "naughty girl," as she sings in a song, or even a "perverse little madonna," as she appears to be when she speaks with anyone as a result of the way she glances upwards at them. One day, Mrs. Mooney begins to suspect that something is going on between Polly and one of the young men, Mr. Doran, who boards in her home. Though others begin to notice the relationship's progression and even Polly becomes aware of her mother's gaze, Mrs. Mooney does nothing to intervene, and the narrator even says that "in this case she had made up her mind." She eventually confirms the details of the relationship with Polly herself; it seems probable that Polly has actually become pregnant with Mr. Doran's child, forcing the matter to a head, and she determines that "only one reparation could make up for the loss of her daughter's honour: marriage."
In the end, despite Mr. Doran's evident apprehension and reticence about getting married, it seems that Mrs. Mooney gets her way. She speaks alone with Mr. Doran and then calls Polly downstairs, saying that Mr. Doran wishes to speak with her. We can divine, from this ending, that Mrs. Mooney has achieved what she'd hoped to: a better marriage for Polly than her own marriage had been. Mr. Mooney went "to the devil" after Mrs. Mooney's own father died, and he became a drunkard who eventually ruined his own business with bad decisions. Mrs. Mooney knows that Mr. Doran is a good man—a godly man from a nice family—and she allows him to become obligated to her daughter in order to make sure that her daughter's marriage is a happier one.