Scooby-Doo! The Mystery Begins

In Coolsville, a pet adoption fair is held and Scooby-Doo is up for adoption. Nobody seems interested in him, and he begins to feel like the odd one out. This moment sets Scooby on a path toward a new home with Shaggy.

On the way back to the pound, Scooby's crate falls off a moving truck and he is accidentally left behind. He wanders the streets seeking shelter from a rainstorm and ends up alone at night. The mishap puts Scooby on a trajectory toward Shaggy's life.

Seeking shelter, Scooby hides in a graveyard and witnesses two ghosts rising from their graves during a rainstorm. He panics and bolts, fleeing into the night. This eerie encounter marks Scooby's first brush with the paranormal in Coolsville.

That night, Scooby slips into Norville 'Shaggy' Rogers's bedroom and the two form an immediate bond. Shaggy, a quirky loner, decides to adopt Scooby and give him a home. The inseparable duo begins a partnership that will drive the story forward.

Shaggy attempts to smuggle Scooby onto the school bus, but a scuffle with a bully leads to chaos. The bus crashes into a flagpole and Vice Principal Grimes's car is damaged. As punishment, Shaggy is sent to detention at the library along with Scooby tethered outside and three other students.

During detention, ghosts suddenly appear and chase the group to the gym amid a pep rally. A cloaked Specter takes center stage and orders everyone to leave. Principal Deedle wants to close the school, while Grimes suspends the four students for the disruption.

The gang tries to clear their names, but Shaggy and Scooby end up locked in the cafeteria freezers. Grimes frees them the next morning and suspends them, threatening arrest for trespassing if they re-enter. They realize the mysteries are bigger than a simple prank.

They sneak back into the school using Daphne's theatrical costuming skills to stay undercover. Velma discovers a spell book recently checked out by Grimes, shifting suspicion away from the students. The group redoubles their resolve to uncover the truth.

That night, at Grimes's house, the gang learns the school grounds were once used by Coolsville Academy and were set to bury a time capsule. The ghosts appear to be pushing the school toward closure so they can search for the capsule unimpeded. The revelation ties the haunting to a town history mystery.

The Specter captures Scooby and Grimes, forcing the rest of the group to search underground for the long-buried time capsule. They navigate flooded tunnels while trying to stay ahead of the vengeful ghosts. The stakes rise as the capsule's location becomes essential to the town's fate.

The gang attempts a setup to lure the Specter away, but the plan backfires when he carries the capsule out of the hole. They scramble to trap him in a flooded chamber, but he escapes with the capsule. The chase shifts back to the surface with the prize in question.

The group recovers the capsule and uses the spell book to banish the ghosts. Scooby arrives at the last moment to subdue the Specter, who is revealed to be Principal Deedle. Inside the capsule, a misprint stamp promises a fortune, explaining Deedle's motive.

Deedle is arrested for his crimes, and the group is reinstated to Coolsville High. Grimes publicly congratulates them and apologizes for not believing their story earlier. The time capsule is officially buried, marking a concluded chapter in Coolsville history.

During the burial ceremony, Shaggy accidentally throws his shovel and damages Grimes's car again. Grimes forgives the accident, noting that accidents happen. The team decides to stay together and continue solving mysteries, ready for new adventures.

With the town's peace restored, the group heads to the Coolsville museum to explore strange goings-on. Their teamwork and curiosity hint at ongoing adventures and the enduring bond of the mystery-solving team. The movie closes on them ready to investigate more.