Canterlot High is hosting a musical showcase and Rainbow Dash, Applejack, Pinkie Pie, Rarity, and Fluttershy are going to be performing with their new band, The Rainbooms. But when a new girl group, The Dazzlings, arrives at CHS, they convince everyone to turn the friendly showcase into a Battle of the Bands. As tensions mount between the competing musical acts, a reformed Sunset Shimmer realizes that the Dazzlings may not be ordinary girls and are after something far more sinister than just being named Best Band at Canterlot High. The Rainbooms call on Princess Twilight to return to their world to help them perform a musical counter-spell so that they can win a battle that now determines the fate of the entire school.