Twilight finds a gender changing spell. No pony has been able to pull it off yet, but she's not just any pony, she's the Princess of Friendship and stands for the Element of Magic! She edits the spell and when she feels like she got it right she looks for test subjects. Afraid of failure and being judged she turns to her friends to help her with this experiment.

When she casts the spell nothing seems to have happened, but given sometime it is clear she has made more progress than anypony else who tried to cast it. The girls change and things get... heated. What will they do when things get out of hand and somepony steals the spell...