Christmas, 1981. At the big holiday house party, 18-year-old Kim discovers that this gathering — with its mixture of alcohol, flirting, and teenage embarrassment — is the perfect feeding ground for the mistletoe-inhabited demon, which seems to be thriving off of the teens’ hormones and anxieties by attaching itself like a parasite. Once it starts growing beneath their skin, their worst fears about themselves come to light, and no can be trusted. Now, Kim and her friends have an almost impossible task — get a grip on their insecurities to defeat this evil force, or face something much worse — death.