Scoob! narrative location Mystery Island
Plot
In Venice Beach, a young, lonely Shaggy Rogers befriends and adopts a young talking stray Great Dane, whom he names Scooby-Doo. On Halloween night, Scooby and Shaggy meet three young children—Fred Jones, Daphne Blake, and Velma Dinkley—before venturing into a haunted house, where they capture a thief disguised as a ghost, which inspires them to form Mystery Inc. and solve mysteries together.
After years of solving mysteries, Mystery Inc. goes into business. During an investor meeting with Simon Cowell, he refuses to do business with Scooby and Shaggy involved due to their behavior, which he insultingly proclaims as childish, and claiming friendship as useless. Infuriated, the pair quit the group and storm out to the Takamoto bowling alley, where they are terrorized by shapeshifting robots called Rottens that belong to Dick Dastardly, who seek to capture Scooby and Cerberus' three skulls. They are rescued by Dee Dee Skyes, and their lifelong idols, Dynomutt and Brian Crown, who has taken over from his father's role as the masked superhero, Blue Falcon. Dastardly and the Rottens trap and terrorize Scooby and Shaggy in a creepy abandoned amusement park, but the Falcon Force rescues them and investigates that Dastardly finds Scooby important, causing Shaggy to feel alone.
Meanwhile, Fred, Daphne, and Velma discover that Dastardly is after Scooby and Shaggy, and head off to investigate. The group also reminisces about the good times they had with Shaggy and Scooby around, before being imprisoned in Dastardly's airship. They escape with one of the Rottens' help and make contact with Dee Dee to explain that she and the others are being taken to Messick Mountain, where the last skull is located. The group then finds out that Dastardly's plan is to open the gates to the Underworld to rescue his dog Muttley, who was trapped during an attempt to steal the Underworld's riches. Dastardly needs Scooby to unlock the gates since he is the last remaining descendant of Alexander the Great's dog, Peritas.
Scooby, Shaggy, and the Falcon Force go underground to a prehistoric island in Messick Mountain. Shaggy, who sees Scooby's importance as an insult to their friendship, wants Scooby to stay with him on the ship. Scooby wants Shaggy to join him and the group, but Shaggy demands Scooby choose between him and them. Scooby picks the Falcon Force, to Shaggy's dismay, and finds Captain Caveman guarding the last skull and testing his bravery, in a fight for it. Dastardly tricks Shaggy into taking him to Scooby and the skull, and captures them, while the Rottens throw Fred, Daphne, and Velma out of the airship. Shaggy expresses guilt and remorse for Scooby's capture, and his speech inspires everyone to work together and rescue Scooby.
Arriving in Athens, Dastardly reveals the Underworld's gates with the three skulls and tries to unlock them with Scooby's paw while Scooby's friends pursue him in a flying Mystery Machine. The Rottens shoot them down, while Dastardly releases the rampaging Cerberus, causing the town to flee. Scooby runs to the crash site to reunite with his friends, and Dastardly reunites with Muttley in the Underworld, and they escape with some treasure. Scooby and Shaggy determine how to trap Cerberus; Fred, Daphne, and Velma determine how to close the gates; and the Falcon Force flies around Cerberus to keep him distracted. With help from the Rottens, they trap Cerberus back in the Underworld, but Shaggy sacrifices himself to stay inside the Underworld and lock the gates, following Alexander the Great and Peritas' bond prophecy. The gang finds an exit that continues the prophecy, which Scooby unlocks to reunite with Shaggy.
The Rottens capture Muttley and Dastardly, who is unmasked twice in a revelation that he impersonated Cowell. The Falcon Force takes the pair into custody, while Mystery Inc. returns home and unveils their official new headquarters. They celebrate their grand opening with the entire town, including the Falcon Force, who gifts them an upgraded Mystery Machine, before they head off to solve another mystery.