Dean finds a case in Stillwater, Minnesota where a 316 pound man was killed in his car and was 98 pounds afterwards. Thinking witchcraft, Sam and Dean investigate, leading them to weird suction marks on the man and another victim. After finding the same mark on a personal trainer, Sam and Dean go undercover at a nearby health spa where people mysteriously lose a lot of weight very fast. While tasting the spa's pudding, Dean gets drugged by roofies and they realize the spa's owner is a monster after Dean catches her eating refrigerated fat. At the same time Sam and Dean confront the woman, Maritza, her brother Alonzo kills her husband after he confronts him about the murders. Maritza explains she and Alonzo are Pishtaco, Peruvian parasitic monsters that feed on fat. Maritza set up the spa to harmlessly feed on human fat from her customers without harming anyone, but her brother wasn't content with that and wanted to feed on people until death. Tracking down Alonzo, Sam and Dean kill him and pass it off as a psycho serial killer to the police. Although Dean wants to kill Maritza too, Sam convinces him not to and they send her back to Peru instead. Later, Dean tries to clear the air between him and Sam about what he did to save him, but Sam points out that Dean did it for himself so he wouldn't be alone. When Dean tries to contend that Sam would do the same for him, Sam tells him he wouldn't, leaving Dean stunned.