Plot
The gang is shown inside a warehouse illustrating a plan to catch the Luna Ghost, (who has gagged and kidnapped Daphne)which goes astray but ends with Scooby and Shaggy causing the Ghost to be caught. After solving the mystery, constant arguments among the members of Mystery, Inc. cause the gang to go their separate ways. Two years later, Shaggy Rogers and Scooby-Doo are approached to solve the mystery of the popular horror resort Spooky Island, reuniting with Fred Jones, Velma Dinkley and Daphne Blake, although none of the latter are thrilled to see each other. On the island, the gang meets Emile Mondavarious, the park's owner, who explains his theory that visitors are being cursed. Shaggy falls in love with a girl named Mary Jane, while Scooby is mysteriously targeted by demonic creatures. Velma meets a man named N'Goo Tuana and his minion, the famous luchador Zarkos, who explains that demons rule the island.

The gang visits the island's abandoned ghost castle, where Daphne finds a tetrahedron-shaped artifact called the Daemon Ritus and Velma and Fred find a strange classroom with videos designed to address non-humans. When the gang returns to the hotel, they are attacked by the island demons, who kidnap numerous tourists including Fred, Velma and Mondavarious. The next day, Daphne is captured by Zarkos, while Shaggy and Scooby discover Fred, Velma and the tourists are now possessed by the demons. The two flee with Mary Jane, until Scooby realizes she is possessed as well. In the midst of an argument between Scooby and Shaggy, Scooby falls down a hole, followed by Shaggy, who dives in to save him. Shaggy comes across a vat containing the protoplasmic souls of everyone who was captured, including the rest of the gang, and releases the gangs' souls to their bodies. Velma discovers the demons are destroyed in sunlight, while Daphne and Fred's souls end up in the wrong bodies.

Shaggy steals the Daemon Ritus and reunites with the gang after their souls correct themselves. Coming across Voodoo Maestro, the gang learns that if the leader of the demons absorbs a pure soul through the Daemon Ritus, then the demons shall rule the world for the next 10,000 years. The pure soul belongs to Scooby, while the demons' leader is Mondavarious. The gang puts their differences aside and finally work together to save Scooby. They form a plan but it fails and Scooby's soul is extracted. Scooby is saved by Shaggy, wounding Mondavarious in the attempt. Fred and Velma discover he is actually a robot, controlled by none other than Scooby's nephew, Scrappy-Doo, who the gang abandoned years ago due to his egotism. Now vengeful, Scrappy transforms into a giant demon to destroy the gang and rule the world using the tourists' souls he absorbed.

Daphne fights Zarkos above the island's caves, knocking him through the roof, which exposes the demons to sunlight and kills them. Shaggy confronts Scrappy and rips the Daemon Ritus from his chest, freeing the souls and reverting Scrappy to his original self. Shaggy finds the real Mondavarious trapped in a hole and frees him. Scrappy and his minions are arrested, while Mystery, Inc. is reunited to continue solving mysteries.

At the end, it shows Scooby and Shaggy eating food at the Spooky Island hotel. They both eat hot peppers and scream as smoke comes out of the hotel.

Box office
Scooby-Doo debuted with $19,204,859 on its opening day and $54,155,312 over the weekend from 3,447 theaters, averaging about $15,711 per venue and ranked #1 at the box office. The film closed on October 31, 2002, with a final gross of $153 million in the United States. It made an additional $122 million in other territories, bringing the total worldwide gross to $275,650,703, making it the 15th most successful film worldwide of 2002.

Critical response
Scooby-Doo received generally unfavorable reviews from film critics and audiences alike. The film holds a 30% approval rating on the review aggregator Rotten Tomatoes, based on 142 reviews with an average rating of of 4.4/10 and the consensus, "Though  Lillard is uncannily spot-on as Shaggy, Scooby Doo is a tired live-action update, filled with lame jokes." Metacritic, which assigns a weighted average score, rated the film 35 out of 100 based on 31 reviews from critics.

Roger Ebert of the Chicago Sun-Times gave the film a negative review, stating that the film "exists in a closed universe, and the rest of us are aliens. The Internet was invented so that you can find someone else's review of Scooby-Doo. Start surfing." Peter Travers of Rolling Stone said, "Get out your pooper-scoopers. Doo happens June 14th, warn the ads for Scooby-Doo. And they say there's no truth in Hollywood." Robin Rauzi of the Los Angeles Times called the film "entertainment more disposable than Hanna-Barbera's half-hour cartoons ever were." Although Jay Boyar of the Orlando Sentinel said that children who liked the animated version of Scooby-Doo will "probably like" the film, he urged parents to "know that the violence is a bit harder-edged than in the cartoon version." He would later go on to say that adults who remember the cartoon version "may get caught up in what Scooby would call the "rostalgia,"" but said that "adults who do not fondly recall the Scooby-Doo cartoons are strongly advised to steer clear."

Conversely, Hank Struever of Washington Post gave the film a positive review, stating that "You don't want to love this, but you will. Although Scooby-Doo falls far short of becoming the "Blazing Saddles" of Generations X, Y and Z, it is hard to resist in its moronic charms."