The Crystal Cove Haunted Historical Society performs reenactments of Crystal Cove history every year. During a rehearsal for this year’s production revolving around Friar Gabriello Serra and his donkey Porto, a specter resembling one of the props scares off the cast and crew members. Vincent Van Ghoul, called upon to take over production, finds the set destroyed and calls in Mystery Incorporated who become the new cast and crew for the play. Meanwhile, Professor Pericles instructs Brad and Judy to steal the Planispheric Disk back from the gang. After solving the case, the gang encounters the real ghost of Friar Serra, who reveals that he was part of a mystery-solving group in the original Crystal Cove settlement named Fraternitas Mysterium, which became a victim of the Planispheric Disk, resulting in the destruction of the original Crystal Cove settlement caused by Friar Gabriello Serra’s donkey. The ghost of Friar Serra warns of the coming of “Nibiru” and that “the dog must die” because the animal mascot always starts the downfall.