Although the play was a success, Luna was very unhappy after she and Celestia returned to the Castle. Celestia doesn't understand why her little sister is acting like such a foal, but Luna is about to give her sister piece of her mind as to why she is so frustrated.

Note that this one piece takes place shortly after the events of the MLP episode "Horse Play". If you have not seen the episode by this time, well, I suggest watching that episode first. Will help make more sense of this story.