The gang drives into a prison, where Morgan Freeman is filming a documentary on its haunting by the Ghost of Jean Lebeau. Somehow, Mystery Inc. becomes a major part of that video and we get an insight into how those meddling kids go about solving a mystery.

A tree monster called the Gnarled One attacks a hot dog eating contest with Joey Chestnut. But the mystery everyone really wants answered is "Who is the best competitive eater?" Is it Joey, Shaggy or Scooby-Doo?