YOH 1490 (Ten Years Before Luna's Return): Eight-year-old Rarity is in danger. Twelve-year-old Applejack is sure that her own parents can save her friend. They're the bravest and strongest mom and dad any filly could have!

But sometimes, even the brave and the strong can fall.

This story is directly based on part 3 of Core of the Apple by Neterrang. I urge you to read that whole comics sequence, starting with part 1. It's one of the best MLP fan comics ever written.

Addendum: This story is now AU (because AJ has different parents) as of "The Perfect Pear." Sic transit gloria mundi.