A production on the sinking of Crystal Cove is attacked by the ghost of Friar Gabriello Serra. Van Ghoul is called upon to revive the production, then calls the gang for assistance. The gang notices George Avacados working as a janitor, and suspects him. With Shaggy and Scooby as the leads, the gang helps put on the play, only for the ghost to attack on opening night. The gang traps it, revealing Avacados to finally be the villain who was searching for the lost Avacados diamond. The real ghost of Serra suddenly appears and explains how he was part of the first mystery solving group, Fraternitas Mysterium, which became a victim of the disk and the curse. It was his donkey Porto who destroyed them all, causing the settlement to sink. Serra warns them of Nibiru, then repeats the warning “the dog dies”, as it is the animal mascot who lead his group to downfall.
