One bright, springtime day, Rarity is appalled and perplexed to see her friends having a party at Sugar Cube Corner without her. She retires, in tears, to her home, only to be saved from her grief by Rainbow Dash, who states that they had, in fact, given her an invitation.

Why wasn't the invitation in Rarity's mailbox? The friends set out on a mission to reveal the mastermind behind all this, expecting some silly foal; the real discovery, however, turns out to be much more sinister. Fighting confusion about their feelings for each other and their other friends, Rarity and Rainbow Dash must find a way to remedy the situation, for the sake of their friendship and the safety of all of Equestria.