Betty Gordon and her friends enjoy Christmas vacation with the Littell family in Washington. While Betty is shopping one day, she meets a girl named Ida Bellethorne, who works in a store. Betty immediately likes the girl, who seems to be unhappy. Betty loses a locket while in the store, and Ida gives it to the owner of the store. When Betty goes to the store again to ask about the locket, the store owner pretends that nothing was found and tells Betty that Ida Bellethorne has gone away. Much troubled, Betty wonders whether Ida could have found her locket and kept it for herself. The time comes for Betty and her friends to return to school—but everyone at Shadyside has the measles! School is postponed for two weeks, and the young people travel with Uncle Dick to Mountain Camp. Although Betty enjoys the vacation, she continues to worry about her locket and Ida Bellethorne. The whole party turned out gaily. Betty unexpectedly encounters Ida Bellethorne at Mountain Camp, and the mystery of the locket is solved. Betty and her friends help Ida Bellethorne become reunited with her aunt just before they return to school.
