The Outdoor Girls' latest adventure takes them to Cape Cod, where they chance to meet two girls, Irene Moore and Stella Sibley, who later move to Deepdale. The girls also make the acquaintance of Sally Ann Bevins, the ward of the lighthouse keeper, Mr. Flood. Sally Ann is practically a prisoner and has been forced to work like a slave for no pay her entire life. The Outdoor Girls want desperately to help her—but how can they help someone too proud to accept help? The girls soon overhear partial details of a plot involving Sally Ann, and Betty writes for Allen's help.