The Night Ghoul of Wonderworld is the second episode of Scooby-Doo and Scrappy-Doo.
The gang arrive at Wonderworld, an amusement park where all fantasies become reality. They meet the host, Mr. Marino, who knows that Velma Dinkley's fantasy is to solve a mystery with Sherlock Holmes. Marino explains to the gang how their visit can be completely safe. He also sends the gang on the Wonderworld train along with an antique collector, Alexander Wallhouse. On their travel, they pass through Jurassic World and Scrappy-Doo's favorite world, Outlaw World.
They finally get to London World, where Velma finally meets Sherlock Holmes who makes her his new assistant while Holmes' old assistant, Dr. Watson, is out of town. At Sherlock's home, Sherlock explained the theft of the crown jewels to the gang. He also told the gang that he suspects an international criminal mastermind, who is also a real monster, known as the Night Ghoul of London. Sherlock led the gang to the London world tower.
They finally arrive at the castle where the gang, except for Scooby-Doo and Shaggy Rogers, entered to check out the crime scene. Outside, Scooby and Shaggy were relieved to see one of the castle guards waiting to capture the Night Ghoul. Unfortunately, the guard was actually the Night Ghoul. They were chased by the Night Ghoul. But when the Night Ghoul fell into the water, Shaggy and Scooby realized that all the robots of Wonderworld can't hurt them, even the Night Ghoul. While Shaggy and Scooby talked to the gang about the Night Ghoul, the Night Ghoul malfunctioned so he could steal the crown jewels that he hid under the display where the Crown Jewels are supposed to be safe. Velma was sorry that the mystery was over so soon until the Night Ghoul appeared, attacked the gang, steal the jewels, and got away.
When the gang and Sherlock got out of the castle, Sherlock told the gang the the Night Ghoul was last seen at the iconic clock of London, Big Ben. When Shaggy, Scooby and Scrappy bumped into the Night Ghoul again, they ran away. Scooby defeated the Night Ghoul, but Velma checked that the jewels aren't in the Night Ghoul's cape. Mr. Marino noticed the Night Ghoul destroyed and suggested the gang to leave Wonderworld. But Velma refused because he hadn't solve the mystery yet. After Marino examined Sherlock, he leaves London world, and wished the gang to enjoy their stay. At the fish and chips store, Velma found another article about the stolen Crown Jewels.
They saw the Night Ghoul again, but he was not a robot. Then he started to get away again. Sherlock noticed that the Night Ghoul went into the bookstore. Scrappy tried to catch the Night Ghoul. But instead he captured Mr. Wallhouse. When Wallhouse left, Fred Jones found the story about the Night Ghoul.
Fred sent Shaggy and the dogs to Big Ben. When they went inside, they noticed a secret room, right above the clock face, where they found the Crown Jewels and the Night Ghoul. They were in a dangerous fight, and when Shaggy reset Big Ben to Midnight, the bell started ringing, much to Fred and Velma's confusion. Sherlock explained to the gang why Big Ben struck midnight but he just blew a fuse, which meant that Velma solved the mystery.
Scrappy made Big Ben go faster to trap the Night Ghoul, and it worked.
Velma explained about a TV antenna at the real Tower of London, so the article describes not Velma's fantasy mystery, but a real crime. The Night Ghoul hid the jewels in Wonderworld but his plans went down the drain when the computer came up with Velma's fantasy. When the Night Ghoul robot malfunctioned, he stole the real jewels and hid them. So the culprit decided to dress up the Night Ghoul to scare people away so he could find the jewels himself. The Night Ghoul is revealed to be Mr. Marino himself, who short-circuited Sherlock instead of examining him.