On a beach, just after sundown, Scooby is sniffing out clams for the rest of the gang to eat. Shaggy comments that he has heard of bird dogs and rabbit dogs, but never a clam dog. Scooby shows his disgust of clams, as he does not fancy them very much. As the gang wind up on their clam hunt, Daphne looks across the beach to the Funland amusement park. She comments about how spooky it looks as it is closed and if on cue, all the lights flick on and the rides begin to operate. The gang head over to investigate.
Before the gang enters, we see a shot of The Man From Mars riding the roller coaster. Shaggy and Scooby then appear and head straight for the hot dog counter where Shaggy pretends to order up a malt and a hot-dog. Mysteriously the two items appear. Meanwhile Fred, Daphne and Velma are at a gaming booth. Fred throws a baseball and knocks down several bottles. Before he can pick them up the bottles are re-stacked and he has won a cupie doll. Fred pays 25 cents and the cash register mysteriously rings up the order.
While Shaggy and Scooby are naturally now trying to eat some cotton candy, they spot the Man From Mars. Shaggy comments that the man is faster than a speeding bullet. Scooby tries to sniff out the man but can’t as he has no scent. Shaggy comments that he must be a ghost. They spot the man walk into the Hall of Mirrors and follow after him. Here they have fun looking in mirrors until Scooby spots a giant mouse and gets scared. Shaggy explains that the mirror just made the mouse look bigger than it really was. Shaggy then sees the Man from Mars standing behind him and they run.
Fred, Daphne and Velma then spot the Man from Mars on top of the Ferris wheel, where the man rides the wheel to the top where it stops. Freddy cranks the cage down, however the robot has disappeared. The amusement park lights all suddenly shut down. The gang decide to visit the caretakers to see if they have any explanations for these mysterious happenings.
At the caretakers home, Mr. Jenkins explains that what the gang just saw as impossible. His Sister, Sarah Jenkins tells them that it was probably the moonlight playing tricks on them. Upset with the caretakers’ double-talk the gang leave their home and return back to the amusement park where all the rides and attractions are running wild.
The hot-dog machine is spitting out wieners and the cotton candy machine is spilling out cotton candy all over as well. They spot the Man from Mars enter the Tunnel of Love and chase after him with a boat. Inside, the Man from Mars swims towards them like a torpedo and the gang all end up in knee deep water. Daphne is extremely mad as her hair has gotten wet. The gang then split up to look for the Man from Mars.
Shaggy and Scooby try not to look very hard and test their strength at a Strength testing machine. The Man from Mars shows up after Scooby and Shag have played and chases them to the roller coaster. While Shag and Scoob sit in the front, the Man from Mars sits in the back car and begins climbing towards them as the roller coaster drives forward. Freddy spots them and slows the coaster down so Shaggy and Scoob can jump onto another coaster. The Man from Mars ends up disappearing however.
Fred has a plan. Since the Man from Mars is so fast, he soups up an electric car to catch the fiend. As he tinkers with the machine, Shaggy sets it off with Scooby and Velma sitting in it. The sudden take off of the car makes Velma lose her glasses and she drives blind, scaring Scooby as they are almost hit by a train. The car ends up stopping in a pile of cotton Candy where it covers Scooby and he licks it off his face with is tongue.
Fred has another plan and makes a crate to trap the Man from Mars in. Scooby is supposed to lure him in while Shaggy locks the door and Velma and Daphne draw Scooby out of the crate with a bucket. Scooby ends up luring the Man from Mars and they run through a museum (where Scooby pretends to be a caveman and a pirate) and then into the crate. Scooby escapes the crate and so does the Man from Mars as he walks through the crate wall and then right through a brick wall.
SPOILERS! ! ! !
Mr. Jenkins shows up and reveals that the Man from Mars is really called Charlie, the world’s most perfect robot. He created Charlie to run the park, however the robot just got out of control. He and the gang then use an electric magnet and a car to catch Charlie. When they do catch him, a hand reaches out and cuts a wire, breaking the electric magnet. The magnet has messed up the Robots wiring however, and he is now dysfunctional.
The gang spot Sarah Jenkins and she admits to causing Charlie to go haywire as robots should not work where children come. Mr. Jenkins acknowledges that she is right and decides to just fix up Charlie and call him Charlie the 2nd. The gang then visit Charlie when he is fixed up and Charlie scratches Scooby behind his ears.