Nancy and pals George and Bess wind up in the town of Penfield, where they visit the Starhurst School for Girls. Once students hear that Nancy, the famed Girl Detective has arrived, they insist she meet Penfield's own teen sleuths, Louise and Jean Dana, the Dana Girls! Soon, a good-natured yet highly involved contest is put together to see who the best mystery-solver is, and it's in the form of a musical complete with clues planted throughout the school. There's only one complication, the "phony" crime concocted for the Mystery Musical turns out to be real!