Pinkie Pie has always been the greatest party planner and thrower of her generation. But when a missing date in a calendar reveals that the birthday of none other than Princess Luna has been overlooked and has been for over one thousand years, Pinkie takes it upon herself to give Luna the best birthday that anypony has ever had. This simple pledge will take Pinkie Pie on a quest against the clock and an ancient secret that upholds the balance of Equestria.