Despite Pinkie Pie priding herself as friend to everypony in Ponyville, she's never seen eye-to-eye with the matriarch of the new family across the way. But her resentment towards the party-pooping Polly T. Burro turns into outright paranoia when the donkey lets slip she knows one of Pinkie's secrets. But how could she? Only four ponies, Applejack, Rainbow Dash, Fluttershy, and Rarity were there for the incident in question, and Pinkie Pinkie-Promised them all to secrecy.

She comes to the conclusion that one of her friends is telling tales. Christening herself 'Smiles' to conceal her identity, she'll have to rely on the help of her erstwhile assistant 'Mr. Gummy-yum' and reluctant librarian Twilight Sparkle to root out whoever's betraying her confidence before her deepest, darkest secret is revealed. But as the tangled web of deceit she's weaving gets stickier and sticker, will Pinkie be able to keep herself from getting permanently stuck out in the cold?