The Ghost of Mr. Hyde steals a necklace and tries to scare off Mystery Inc. as they investigate.
A jeweled necklace is stolen from a museum by the Ghost of Mr. Hyde, who evades capture by hiding in the back of the Mystery Machine. When he's discovered by the gang, they follow him to the home of Dr. Jekyl.
Dr. Jekyl, a vitamin scientist, reveals that he's afraid he may be the ghost, as a result of personally testing his latest formula. The gang decides to search his home for clues, at which point the Ghost of Mr. Hyde chases Shaggy and Scooby. Fred, Daphne and Velma meanwhile discover a newspaper clipping, partially burnt in a fireplace, with an article about a famous trapeze artist named Helga the Great. Thinking Helga the Great must be Dr. Jekyl's housekeeper, Helga, the trio decide to search her room, where they discover suction cups, face paint and vitamin pills.
At the bottom of the stairs, as they're reviewing their clues, Shaggy and Scooby crash into them and the decision is made to catch the ghost. Shaggy and Scooby lure him down a hall which has a trap door Fred is able to send him down. The unmasking reveals him to be Dr. Jekyl, who had turned to a life of crime after his experiments all failed and was framing Helga.
- Security guard
- Sheriff (no lines)(single appearance)
- Malt Shop
- The marsh
- Dr. Jekyl's mansion
- Helga's room
- Jeweled necklace
- Test tubes
- Vitamin formula (mentioned)
- 101 Ghosts and Ghouls book
- Newspaper clipping
- Face paint
- Vitamin pills
- Suction cups
- The Mystery Machine
|Helga||Evidence discovered in her bedroom.|
|Dr. Jekyl||To steal jewels after his experiments failed.|
- The book features eleven activities, including a crossword puzzle, mazes and a cut-out Ghost Clown mask.
Inconsistencies/continuity errors and/or goofs/oddities
- Besides removing scenes/lines, several elements of the original episode are altered in this adaptation:
- Dr. Jekyll is renamed Dr. Jekyl.
- The Ghost of Mr. Hyde robs a museum, instead of a department store.
- The home of Dr. Jekyl is far cleaner and newer-looking than it is in the episode, where it appears to be fairly old and cobweb-filled.
- Dr. Jekyl makes no mention of his relative being the original Mr. Hyde, simply pinning the blame for his transformation on his vitamin formula testing alone.
- Shaggy and Scooby run into the Ghost of Mr. Hyde before Fred discovers the newspaper clipping, instead of after.
- The newspaper clipping has been edited to read "famous trapeze artist will give a special performance of her human fly act", while the original said "famous acrobat and trapeze artist - Helga - will give a special performance of her human fly act".
- The title of the book Shaggy finds has 101 written numerically, instead of spelled out as "a hundred and one".
- Shaggy and Scooby crash into Daphne and Velma at the bottom of the staircase, instead of just Velma.
- Only Fred, Daphne and Velma search Helga's room, whereas Scooby-Doo joins them in the original episode, with Shaggy standing just outside.
- The clues they discover in Helga's room are face paint, vitamin pills and suction cups, while the episode has them finding only phosphorus paint and a bottle of knock-out drops and Shaggy discovering the suction cups in a fruit bowl in the hallway.
- Shaggy sings "For he's an ugly masked fellow, that nobody can deny.", altered from "For he's an ugly bad fellow, that nobody can deny.".
- Fred pulls a lever, dropping the Ghost of Mr. Hyde down a trap door in the hallway in order to catch him, but in the episode they disguise themselves as multiple ghosts of Mr. Hyde and scare him onto a trap door outside, on the front porch, which opens on its own.
Fred: There you guys are, and just in time! The Ghost of Hyde is a 24-carat phony. Now it's our turn to scare the hide out of Hyde.