After a chance encounter with a bat species she's never seen before, Fluttershy gets bitten, and strange things start to happen. All normal food tastes foul to her, and instead, she thirsts for blood. As she slowly becomes more animalistic, her instincts heighten, and suddenly the feelings towards Rainbow Dash she'd been suppressing slowly begin to manifest. After a failed attempt to seduce her in order to feed, Rainbow Dash becomes committed to helping Fluttershy get well again while keeping her friend's dark affliction a secret.