Rarity's got a dirty secret she's hiding from her friends. She suffers from an antisocial personality disorder, which means she has no feelings of remorse for any bad thing she does, even if it hurts her friends. When Rainbow, Twilight, and Fluttershy grow concerned for her health, they decide to check up on her. Rarity ends up snapping and taking all her rage out on them, leading to Rainbow Dash making a huge mistake in means to protect herself.