Plot

The gang goes on a trip to check on Velma's younger sister, Madelyn. She's been studying stage magic at the Whirlen Merlin Magic Academy, where apparently there have been sightings of a giant griffin. The gang decides to investigate.

One evening, a couple bird watching in the woods come face to face with a gryphon. After helping the Mystery Gang solve their latest mystery at a factory, Velma receives a call from her mother asking she check on her younger sister Madelyn, who attends a college for magicians and informs her about the Gryphon. The gang heads to the Whirlen Merlin Magic Academy, located into an old Irish castle. Once they reach the castle they meet the owner, Whirlen Merlin, along with his brother Marlon, who acts as cook and butler, and Crystal, Whirlen's former stage assistant. The gang learns that the gryphon has been scaring away the students and academy staff.

Later that evening, Madelyn, who has a crush on Shaggy for years, takes him on a romantic trip into the gardens and shows him an ancient sundial. Madelyn explains the gryphon was meant to protect the school, but then the gryphon chases them from the garden. The rest of the students leave, so the gang begins taking classes themselves. Meanwhile, Calvin Curdles, a powerful ice-cream guru, continually offers to but Whirlen's castle from him. The gang promises to investigate if Curdles is behind the attacks of the gryphon.

Velma and Daphne stumble on a secret passageway leading to the attic of the school, where they discover Alma Rumblebuns, the school's head maid, used to date Calvin Curdles. Meanwhile, Shaggy and Scooby discover the special effects room of the castle, where they are discovered by Ms. Rumblebuns and knock over some chemicals, creating a fog. Madelyn then finds a book about the ancient staff of Lord O'Flannery, the original owner of the castle, which is said to control the gryphon. Even though Amos warns them the island where the staff rests is haunted by a banshee, the gang travels to O'Flannery's crypt and recover the staff, but they are chased away by the banshee and narrowly escape.

Afterwards, the gryphon quickly appears again. As the gang run into the castle, Shaggy and Madelyn bump into Amos and misplace the staff with Amos' pitchfork. When Madelyn runs outside to recover the staff, she is kidnapped by the gryphon. Meanwhile, the gang finds out that Amos has been secretly working for Calvin Curdles to attempt to have Whirlen to sell the castle. While the gang goes to rescue Madelyn, Calvin renews his attempts to convince Whirlen to sign over the castle.

They get into the tower with the staff and learn the banshee is a video projector. They are then separated in the process when the gryphon attacks. Shaggy and Scooby are abandoned while the others get help, and Shaggy discovers the staff is a key to the roost where they rescue Madelyn. But their reunion is quickly cut short when the gryphon attacks, but they are able to escape. Shaggy also throws the staff at the gryphon during the process, causing this to go out of control. Everybody else rushes inside including Curdles. The gryphon crashes to the ground, where they discover this is actually a giant puppet, controlled by a blimp hidden by a fog machine managed by Whirlen's brother Marlon. He had discovered O'Flannery had mechanical devices imitating a gryphon's beak and talons hidden in the Gryphon's Roost, hoping this would make everyone think a real gryphon resided their. Marlon repaired then, and used the devices to scare away trespassers. He was also behind the banshee, which was only a hologram.

Annoyed of doing all the real work but getting none of the credit, Marlon decided to use his puppets and illusions to become famous magician himself, but her needed money to begin and the only way was to have Whirlen sell the castle. So Marlon had his gryphon puppet scare away everyone. He apologizes for attempting to make Whirlen fail, knowing how much the school meant to him, not wanting to take away his dream. Whirlen forgives Marlon, and a happy ending makes up for everything that happened before. Velma reveals Amos found Marlon rebuilding the gryphon and informed Curdles about this. Curdles reveals he wanted to buy the castle to win back Alma's heart. Alma accepts him back and they become a couple again. The Merlin brothers decide to make Madelyn their apprentice and soon after, Calvin Curdles sponsors the reopening of the Merlin Brothers' Academy of Magic, where Madelyn performs with Daphne acting as her assistant.