Doug, a dorky young mamma’s boy, who is about to get married to his beautiful bride, Callista, when he notices a change come over her. He catches her sneaking around at night and lying to him, and she’s begun to display flu-like symptoms. So naturally Doug thinks she caught a disease while cheating on him. In reality she has become possessed via an ancient stone and she’s been eating his friends and family without him knowing.

Scooby-Doo and the gang are on the case when a mysterious lake monster starts scaring the guests at a summer resort in Erie Point, where Fred, Daphne, Velma and Shaggy have taken on seasonal jobs to pay for a barn they accidentally burned down. But in addition to sneaking suspicions, there’s some romance in the air.