It's the 10th anniversary of the BFFL becoming friends and nothing can break them up... except a new girl in town named Garnet. She befriends Amethyst, Sapphire, Topaz, and Onyx one by one while ostracizing Ruby, making the latter jealous, lonely, and angry. Ruby goes to investigate and finds that Garnet is mean to her own mother, making her suspicious and concerned. Garnet continues to exclude Ruby, spreading rumors that she cheated on a test, and appoints herself the new leader of the BFFL. When Ruby's friends try to cheer her up with spells, they mysteriously backfire, making her feel even worse and more suspicious of Garnet and her mother.
Ruby can't find more proof than that, though, until she goes to Garnet's house while they're away. With a spell, she sees Garnet and her mom making a batch of foul-smelling cookies for her friends... and that they're Simon and Snarf in disguise! At the Mystic Waterfalls, they feed the four girls the cookies, which brainwash them. Ruby arrives and is able to avoid eating the cookies, and snaps her friends out of it by pointing at the magic waterfall's reflection, letting them see Simon and Snarf's true forms. While the cookies' powers have paralyzed the other girls, Ruby manages to use a lightning spell to chase Simon away and save her friends. They apologize and gratefully welcome her back into the group.
This episode contains examples of:
- Ambiguous Syntax: When "Garnet" tries to spread a rumor that Ruby cheated, Topaz thinks "she" meant that Ruby cheated on Rock, when "she" meant that she cheated on a test.
- Hypnotize the Captive: The girls are brainwashed by Simon's cookies into avoiding Ruby.
- Mind-Control Eyes: The girls get these when they eat Simon's cookies and are brainwashed by them.
- Spotting the Thread: Ruby notices very subtle things that clue her into Garnet's true identity, like her door knocker being shaped like Simon's bow tie and the cookies Snarf made tasting like dog food. She fully pieces it together by casting a spell to see who they really are.
