Shaggy and Scooby-Doo are haunted by The Ghost of Mrs. Shusham, the librarian who wants an extremely overdue library book back.

When the famed ghost-busting group "Critter Getters" breaks up, the Scooby-Doo Detective Agency gets hired to find a way to get them back together so they can find out who's hiding in the costume of the "Moving Mollusk" that's terrorizing New York.