The American Grand Opera has come to River Heights to perform Tosca, Aida, and The Marriage of Figaro, and Nancy's friend Bess is going to be a chorus extra. It's all so exciting for the girls; the costumes, the music, the glamor! Little do they expect, though, the drama that will take place backstage. When a falling sandbag from the scenery catwalk nearly misses the two female stars of the opera during a dress rehearsal. Nancy begins to suspect foul play. As it turns out, the falling sandbag isn't the first incident of the tour. In the dressing room, Nancy finds out that rival singers Rosacrucia Alba, the hot new soprano, and Marta Willentz, and older member of the company, have been involved in a few scary situations. As rehearsals continue and the threat to these singers increases, Nancy scrambles to determine why someone is trying to ensure that only one singer will be the star of these shows.