When Rainbow ends up stuck in a hospital bed after flying through an unschedualed, violent storm, she gets to know the mare in the bed next to hers. A light grey pegasus named Derpy. A pony who tries so hard to learn, so hard to understand the world but has difficulty remembering and processing new skills. A pony who's wanted nothing more all her life than to be smart, accepted, normal.

When news of a new experimental spell said to increase intelligence begins to spread, Derpy is the first to jump at the idea. Rainbow does everything in her power to help her friend, and with some encouragement from Twilight, the wall-eyed mare is chosen for the experiment.