The "Ghost Truck" is the third villain of Scooby Doo: Mystery Incorporated.
Late at night, a cop is talking to a young man about how fast he was going. Suddenly, a truck zooms by, and the officer goes after it. He tries to pull it over until he sees no driver, the truck then runs him off the road, sending his bike into the sea below.
Later, Fred, Daphne, Velma, Shaggy, and Scooby are returning home from city hall, when they are attacked by the Ghost Truck. It rams them off the road, and they land on another road below. They think they are safe, until they see the Truck coming down after them. They speed away, eventually entering a tunnel. The Truck tries to smash their car against the wall, but they make it out of the tunnel and quickly pull over, letting the Truck pass and speed off into the fog.
Later, the gang is tailing George Avocados, who is running for Mayor against Fred Jones Sr., the previous mayor. They believe him to be the Ghost Truck's driver, and as they lose Avocados in the fog, they come across the parked Truck. Inspecting it, they see that while it looks ancient, it is practically new. Fred begins to climb the truck, but it starts up, and they get in their car and drive off in reverse. Fred parks the car behind a large rock and turns off the headlights, and the Truck goes right past. They follow the Truck's tread prints, and find that they come to an abrupt end at a wall. Daphne finds a hidden switch, which reveals another switch that Velma and Fred activate, revealing another switch that Scooby activates, finally opening the wall. In the secret cavern, they discover piles and piles of the town's missing crystal doorknobs. Daphne finds the diary of George Avocados' father, who stole a priceless diamond from the bank and swapped it out with a crystal doorknob. They realize that Avocados must be stealing all the doorknobs to try to acquire the diamond. Suddenly, the Truck appears in the cavern, They get in the car and lead the truck into town to city hall, where Fred has built a trap for the Truck. The trap is set off and is successful in flipping over the Truck. The gang watches as Rung Ladderton, not George Avocados, climbs out of the Truck. He explains that his motive was to get rich, as he owns a ladder company, and ladders are something that doesn't get replaced often, so not a lot of money was made. He wanted the diamond to become rich, but as the diary did not state which door the diamond was on, Rung simply stole all the crystal doorknobs, using the Ghost Truck to ship them to his secret cavern while scaring off investigators.
Rung would have gotten away with it if it were not for his meddling peers. Daphne takes Fred's scarf and puts it back for him and Rung is sent to jail.
Scooby-Doo Mystery Incorporated