Years ago, Rainbow Dash achieved her lifelong dream of becoming a Wonderbolt. She'd gone through the academy, been a staple of the main lineup and earned the rank of Captain, and at 43 years of age, it's time for Rainbow to leave that dream behind.
Celestia has been alive for thousands upon thousands of years, and as a result, has had more than one student who have studied under her. When her long dead students appear in modern day Equestria in their youth, Twilight must discover why.