Case History: The gang happen on an accident scene involving a midget and a strongman who are fleeing a circus that appears to be under a curse. The gang visit the circus and find that it is being haunted by a "ghost clown." After the rest of the gang leaves, they discover that they have left Scooby behind. They return to the circus, where they find that he is in a trance and walking on the tightrope high up in the big top: he has been hypnotized by the ghost clown. Shaggy and Velma manage to save him.

Searching another part of the circus, Freddy and Daphne spot the ghost clown and follow him into the costume tent, where Freddy is pushed into a trunk and Daphne is hypnotized by the ghost clown. Shaggy, Velma and Scooby spot Daphne riding a unicycle and wake her up. After rescuing Freddy, they try to trap the ghost clown in a cage. But the ghost clown puts Shaggy in a trance and sets him taming lions. After Sccoby rescues Shaggy, they lead the clown to the trap, but he vanishes from inside it. Freddy's frustrated cry of "I would have bet money we caught him!" unlocks Shaggy's memory: the ghost uses a gold coin to hypnotize his victims. Going out again, Scooby and Shaggy use mirrors to turn the ghost clown's hypnotic tricks back on him and cause him to act like a chimpanzee. He is unmasked as Harry the Hypnotist, a former performer at the circus who was fired and sent to prison after being caught stealing.

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