- Directors: Raja Gosnell
- Producers: Charles Roven, Richard Suckle
- Writers: Screenplay, James Gunn, Story, Craig Titley, James Gunn, Characters, William Hanna, Joseph Barbera
- Genres: Adventure, Comedy, Family, Fantasy, Mystery
- Actors: Freddie Prinze Jr, Sarah Michelle Gellar, Matthew Lillard, Linda Cardellini, Rowan Atkinson, Isla Fisher
After solving the case of the Luna Ghost, an unco-operative Mystery Inc., consisting of Fred, Velma, Daphne, Shaggy and Scooby-Doo, splits apart. After 2 years, Velma has been an advisor at NASA, Fred has become a popular celebrity, Daphne has become a skilled martial artist, and Shaggy and Scooby have stopped investigating mysteries. The gang is surprisingly reunited when they are all summoned to Spooky Island, a monster-based theme park on a remote island. While Shaggy and Scooby wish to work together as team, the others are not as enthusiastic. On the plane ride there, Shaggy falls in love with a girl named Mary Jane, who likes Scooby Snacks and is allergic to dogs. On Spooky Island, the gang meet Emile Mondavarious, the eccentric owner of the island. He explains that visitors to the island come but leave as emotionless and almost inhuman (as demonstrated when a girl picks up an older man and throws him away with one arm).
Since they are still upset with each other, none of the former Mystery Inc. members want the others to solve the mystery first, so they all split up to search for clues. Velma witnesses a creepy dance in which a man named N’Goo Tauna and his servant, Zarkos (A.K.A. The Masked Luchador wrestler) explain that demons once ruled the island until Mondavarious built the theme park on it, enraging the demons. Velma is unafraid of N’Goo’s threats of vengeance. Daphne meets Voodoo Maestro who quite clearly warns her not to go the Spooky Island Castle attraction, but she believes he is setting a trap for her there and goes to spring the trap. The gang meet up at the castle and split up to search for clues as group. Fred and Velma discover a strange classroom with a training program describing how to act like a human. Daphne finds a strange triangular artifact called the Daemonritus. Then after Scooby belches quite loudly, he and Shaggy then get into an exaggerated belching contest that then turns into a farting contest where both do both quite loudly and with exaggerated mannerisms (and Scooby reacts to the smell). Moments later, Shaggy farts again and it echoes in the suit of armor he’s wearing, while the gas briefly ignites over an open flame.
Fred and Daphne kiss as a victory. Scrappy, N’Goo, Zarkos and the other minions are arrested, and Mystery Inc., now completely back together again as a more equal team- particularly reflected when the formerly arrogant Fred allows Velma to explain their line of reasoning for the news teams-, head off for their next case. In the final scene, Spooky Island seems to be back to business with Scooby and Shaggy enjoying the “all you can eat” that was promised to them when they were invited to the island.