When Rainbow Dash finally receives the news she's become a Wonderbolt on the exact day predicted by Star Catcher, the latter thinks this will finally resolve their differences once and for all. Much to her surprise, Rainbow Dash reacts hostilely and blames her for the perceived delay. One thing leads to another, and the two end up exchanging jobs. Star Catcher takes Rainbow's place on the Wonderbolts, while Rainbow Dash becomes the new Duchess of Cloudsdale.

A classic 'fish out of water story.' Hilarity ensues... right?

Not quite. Much to the dismay of those around them, both prove to be proficient in their new careers. Will things go back to normal, or have these two ponies changed things permanently?

Third in a series, I'd advise reading the prequels first:

https://www.fimfiction.net/story/170182/hysteria (optional)

https://www.fimfiction.net/story/138381/if-wishes-came-true (Star Catcher's story really starts here)