In present-day Equestria, Sweetie Belle collapses while playing with her friends, and is discovered to have an incurable heart condition which leaves her with only a few months left to live.
Desperate to help the filly, Twilight spends the next several weeks secretly researching and constructing an apparatus that will allow her to take Sweetie Belle hundreds of years into the future, at which point she believes that medical science will have advanced far enough to cure Sweetie Belle.
The time travel jump is successful, and Twilight and Sweetie Belle end up 350 years in the future, in an Equestria rather different from their own. Sweetie Belle is quickly given an operation to replace her defective heart valve with a mechanical one, which is a complete success.
There's only one problem; the time travel apparatus was destroyed in the process of transporting them to the future, leaving them stranded with no way to return to their own time. She and Sweetie Belle are now trapped in the utopian future Equestria, a world where technology has advanced far enough to be almost indistinguishable from magic.
- Failure Is the Only Option: All of Twilight's attempts to reconstruct the time travel apparatus fail, and Celestia suggests that it is, in fact, impossible for her to do so.
- Fish out of Temporal Water: Twilight Sparkle and Sweetie Belle.
- I Choose to Stay: A reluctant example. Twilight eventually accepts her new life in the future after realising that she's missing Sweetie Belle's current life by persisting in her efforts to return home.
- Ill Girl: Sweetie Belle.
- Shout-Out: Sweetie Belle stars in a stage play based on another MLP fanfic by a different author.
- Stranger in a Familiar Land: The future Equestria is almost unrecognisable to Twilight and Sweetie Belle.
- You Can't Go Home Again: It's not clear until the end if Twilight and Sweetie Belle ever will be able to return home.
- You Can't Fight Fate: The last chapter is even titled You Can't Change The Past. This is set up for a subversion in the previous chapter when Twilight has a revelation regarding her time machine, but in the end is revealed to have been played straight all along: Celestia simply lied when she said Twilight never returned, in an attempt to be with her longer.