Lancaster in the Pennsylvania Dutch country is the scene of a present day mystery that takes on a certain individuality from its setting, however hackneyed the plot. Merry, 16, and her cousin Jinny from the South are heroines in the case. Merry lives with her father who is Lancaster's market master, and when Jinny arrives the two girls notice strange things. There are mysterious lights in the market place, and Mr. Sloan, who lives upstairs, beats his son and badgers his wife. With help from the Dietrich boys who live in the country, the girls solve a double problem for the lights lead to a jewel theft, and Tommy, who is not the Sloan's son at all, is given a new home when the reasons behind his father's misbehaviour are disclosed, District customs are interjected between the lines, but they are little excuse for the stilled and predictable all's well that ends well.