Princess Celestia's birthday is coming up and Twilight wants to make her a party. A surprise party. She asks Pinkie for help but an accident disposes of Pinkie for a short while and she leaves the mare alone to plan the party by herself. Knowing she won't be able to make the party as fun as Pinkie could she turns to her friends for help but all of them are busy.
She turns to a a special crystal recording that Pinkie left titled... "Being Pinkie Keen!" With the help of the crystal recordings can Twilight learn to loosen up and be more like Pinkie? Or will she fail?
Read the first two installments to get some of the stuff mentioned. Cover image is from here: http://ks4u.deviantart.com/gallery/33897448#/d46gleu