When Princess Luna must leave Canterlot for a few weeks, she decides there is only one pony she trusts enough to care for her precious student: Twilight Sparkle. Unfortunately, she forgot to mention a few things. Things such as, 'don't let her near the Cutie Mark Crusaders'. Eh, those are just minor details... Right?

"Diamond Tiara has had a tough life but nopony notices. She's rich, popular, adored. She must be happy. Right? Not always. Diamond Tiara tells the true story of her life through a letter. A letter to nopony"