Penny, plagued by body dysmorphia and binge eating, impulsively takes Thinestra, a mysterious weight-loss drug. That night, she violently expels masses of fat in a grotesque purge. But her discarded fat returns, and like the Hyde to her Jekyll, Penelope is born. As her ravenous dopplegänger wreaks bloody havoc, Penny struggles to regain control. Can she overcome her hunger before it's too late?