Given Supernatural's penchant for its overarching plotlines, the occasional old school "monster-of-the-week" episode serves to remind us that while the Winchesters are off fighting angels and demons, monsters are still abroad and need hunting!
The Purge saw the Winchesters investigating a couple of bizarre murders where the fat was sucked out of the victims' bodies. A bit of legwork led them to a health spa run by an enthusiastic husband and wife team.
The brothers go undercover, with Sam as a fitness instructor and Dean working in the kitchens, and the nature of the monster was quickly revealed - a Peruvian pishtaco (yes, it's a real thing) - but naturally there's a twist in the tail.
Aiding, in her own small way, the Winchester brothers was Fargo-esque Sheriff Donna Hanscum (Brianna Buckmaster), who I gather we'll be seeing again next season. Donna was another nice character with growth potential who joins Sheriff Jody Mills as a strong, supporting character in the Supernatural-verse.
The theme of The Purge, continuing from last week's Sharp Teeth, was about monsters trying to live productive lives within human communities and then the hunters' reaction to that revelation - after all, monsters are monsters, argues Dean.