While visiting his sister Twilight at her home in Ponyville, Shining Armor is accidentally transformed into a little, blank flanked filly. In order to hide her mistake while she tries to find a solution, Shining Armor must live as Twilight's little cousin Gleaming Shield. Things get worse when the Cutie Mark Crusaders meet the new filly and decide she needs to join their group in their adventures around town.

Thanks to DDRMASTERM for taking the time to edit the story

A Cutie Mark is meant to represent the personality and special talent of each pony that has one. Cheerilee's flowers symbolize her desire to help her students bloom, and the smiles represent the cheer that she hopes to bring to their lives.

At least...that's what she tells everypony who asks.

[SEMI-SAD]

Derpy has spent the last few weeks holed up in the library's basement with permission from Twilight. The only problem is, Twilight wants to know what Derpy is doing and she isn't telling. So, the only logical course of action is for Twilight to find out on her own.