So basically the plot is that there are these three lasses called the Sirens who feed of bad energy between friends to get a better voice which gives them more power. The mane six come back together with Sunset Shimmer as the seventh wheel who is still distrusted by the whole of Canterlot High.
So the mane six challenge the sirens at the battle of the bands. It all goes wrong however! Meanwhile Sunset Sparkle is not involved in the band and tries to fix the discord is fixed between the mane six who are starting to fall out. So they all start to prepare for the second round. Sunset Shimmer is onto the tricks of the bully sirens and they begin to bully her because nobody wants to be her friend.
The second round ends with all the school falling out trying to prove their personal superiority and feeding the sirens' powers. This continues as the rounds progress and Sunset Shimmer is visibly upset that Twilight Sparkle cannot find a counter spell to beat the sirens.
It becomes clear that if the Rainbooms are to win the battle of the bands then they need to include Sunset Shimmer. They do not realise this however. Indeed she tries to stop Rainbow Dash from showing her magic but alienates everyone who now believes Sunset Shimmer is a jealous beast who has reverted to her own ways. Yet the mane six still go through because of the bully sirens enchantment over the principles. The sirens must defeat the mane six to top off their power.
The sirens then trick Trixie into trying to hinder the Rainbooms so that they alone may win without even having to face the mane six and sew yet more discord. The mane six get locked under the stage by Trixie and fall out while she performs her set. All their magic then goes to the Sirens who begin their performance.
Sunset Shimmer helps fix their problems and Twilight realises what must be done. They must play together as friends! Then they interrupt the bullies' set and transform into the 'EQUESTRIA GIRLS! They battle one another through music.It gets really intense but the Rainbooms manage to win with the help of Sunset Shimmer who sings her song and they all rally together. EvePost too long. Click here to view the full text.