Main is a girl (perhaps a name like Julia or Nadis), and she falls for the main protagonist of this school play. Joins the theater club to get close to him, but finds out things aren't exactly what they appeared to be on the surface. She meets the boy who played the antagonist, who she just so happened to notice in the play, and he turns out to be really nice. He enjoys theater, is loyal, and isn't really dark-and-mysterious like she originally thought. Then she meets the boy who she was crushing on and slowly learns that he's a jerk. He bullies kids, is an entitled prick and is generally what one would expect of a villain.
The girl tries to interfere with the play's next production, and ends up finding a way for the the antagonist boy and the heroic boy to switch roles. They do, but neither is comfortable with the change. Eventually, during the final production they decide to just wing it, completely abandoning the story line and making it that the heroine was actually the villain all along, and that the princess was actually an evil sorceress. In the end she finds out that the boy she was crushing (Hero) on already had a girlfriend; and in an act of defiance she kisses the other boy (Villain) right there.
*Make sure to sprinkle a bunch of mind games between antagonist boy and main girl throughout the story that alludes to them being friends and him maybe being gay. (Its a subplot possibility).