The entire town is excited about the summer music festival—especially the Aldens, who have been asked to help with the show. The largest attraction this year will be the popular Greenfield Four. A big-time music producer is going to be in the crowd to catch the show, and Greenfield residents hope their favorite local group will be famous soon. The day before the show, The Greenfield Four arrive at the rehearsal hall to find all of their instruments missing! The band insists that they won't play without them, and now it's up to the Boxcar Children to find the instruments before the show. Who would want to sabotage the band's big show? Does someone want to steal the Greenfield Four's spotlight, or is the theft an act of revenge? The Aldens are on the case in this music festival mystery.