As the episode starts, a woman named Carla Canterville, living in an old castle (as always, the same old castle from every other episode) finds her daily household routine and chores constantly disrupted by what she assumes is the resident ghost of her ancestor, Sir Simon De Canterville. In fact, it is international jewel thief Mister C, plotting to drive Carla out so he can tear the place apart looking for the lost Canterville Diamond. However, Sir Simon is present in the house, and when an exasperated Carla runs off to find someone to get Sir Simon out of there, the cowardly and jumpy Simon is actually grateful for the effort—so long as whoever she gets isn't too scary.
In the meantime, Jake Kong returns to the Ghost Busters run-down office to find Eddie Spenser and Tracy The Gorilla engaged in their usual nonsense, till he chases them out to go get their next assignment recording from Zero. Informed of Carla's seeking them out (and, presciently, that things may not be as they seem in this case), the trio meet her at the door, as she first faints at the sight of and then quickly befriends Tracy. Repeatedly, Carla is interrupted as she tries to tell the hapless heroes that their usual method of banishment will not work in this case, till they actually meet Sir Simon, who cowers in fear at the sight of them. A coward in life, the only way Sir Simon can move on is to commit one brave deed, and he again proved his cowardice by running off into the castle at little or no provocation.
In hiding (inside a terribly obvious 'moving eyes' painting and a badly-disguised secret passage) Mister C briefly sights Sir Simon, wearing the diamond the thief has targeted. Thinking his new target is some sort of magician (he saw him disappear, but apparently doesn't believe in ghosts), and resolves to get rid of the others. He tries to do this by wearing a suit of armor from the castle, but only succeeds in briefly getting rid of the hapless Eddie—his efforts to scare or knock out Tracy understandably fall short, and the others give chase. Briefly when Sir Simon drops the Diamond, Mister C steals it and tries to hide in his now-exposed secret passage. Aided by an old-fashioned antique radio somehow charged up by the adjacent Ghost De-Materializer, they force Mister C out of his hiding place. During all this, as Tracy gently tries to calm a flustered Carla, Sir Simon sees only the gorilla assaulting his descendant, ineffectually attacking and badly confusing the heroic gorilla. In addition, when Mister C runs by them, Simon stops him from pushing Carla down, and as Mister C is taken in, Sir Simon's conditions are met, his curse is broken, and Mister C is taken to jail for a long stretch. Oddly, despite having the existence of ghosts confirmed right in front of him, Mister C never reacts to this.
- Zero's prescience in knowing the details of this case has a good meta-explanation : The never-seen employer of The Ghost Busters is also their real-life employer. Zero is voiced by Filmation founder and perennial voice actor (such as He-Man's King Randor) Lou Scheimer.
- In this episode, The Ghost Busters aid an innocent, well-meaning ghost against a corrupt Human, something that would happen again more than once to their in-name-only counterparts on the 1980's animated series The Real Ghostbusters.
- According to Wikipedia and IMDB, this episode is a sitcom and voice acting bonanza :
- In addition to regulars Forrest Tucker and Larry Storch, formerly of F-Troop, Mister C was played by actor Len Lesser, who had some experience with the ghoulish on The Munsters, and with the comically surreal as Jerry's Uncle Leo on Seinfeld.
- Sir Simon was played by Filmation pillar Ted Knight, aka Henry Rush of Too Close For Comfort and more iconically, hapless antagonist Ted Baxter on The Mary Tyler Moore Show. Knight and Storch had worked together before, as the first animated voices of Batman villains Penguin and Joker.
- Carla's actress, Kathy Garver, had played eldest sibling Cissy on the sitcom Family Affair (which may or may not be where Joss Whedon got the names Buffy and Giles) for five seasons and was the voice of 80's animated Marvel superheroine Firestar on Spider-Man And His Amazing Friends.