The film opens with the original song "Trick or Treat" playing, as Witch Hazel is shown flying around town on her broomstick (named "Beelzebub"). She comes across Huey, Dewey, and Louie trick-or-treating, dressed as a ghost, a devil, and a wizard. Hazel looks on as the trio go to their Uncle Donald's house and ring the doorbell. Donald, seeing them through the window, decides to prank the boys. So instead of giving them candy, he puts firecrackers into their bags. After the firecrackers explode, Donald pulls a string which tips a bucket of water on the nephews, soaking them. Donald laughs uproariously, but Witch Hazel decides to get even.
Hazel consoles the three, and, delighted to discover that they believe in witches, agrees to help them get their candy from Donald. They go to the door a second time, but Donald refuses to believe Hazel is a real witch. He tries to pull her nose off and again dumps the bucket of water on her. He again laughs hysterically and slams the door. Hazel decides getting the candy from Donald may be harder than she realizes, so she turns to her magic.
Back at Hazel's home, she concocts a magic potion in large black cauldron. In a scene paying homage to William Shakespeare's MacBeth, Hazel adds ingredients to the pot, although they are somewhat toned down from Shakespeare, such as "Eye of needle, tongue of shoe, hand of clock that points at two!" etc. When the potion is finished, she fills a spray bottle with it and flies back to Donald's house with the nephews.
As Hazel sprays various items around Donald's house, they become animated or anthropomorphic. Donald is terrified and instantly agrees to treat the boys to candy. However, when Hazel refers to him as a pushover, he changes his mind. Donald locks the pantry door and swallows the key. Having been "itching" to put a spell on Donald, Hazel uses the potion to put Donald's feet in her control. She orders the feet to kick the key out of Donald, which leads him to perform a wild dance. The key is retrieved, but Donald throws it into the pantry, under the door. Enraged, Hazel then casts "a spell that's double-grim!" saying that she will order Donald's feet to "smash that door down" with Donald. This is initially unsuccessful, so she advises that Donald "take a longer start. About a mile or two!" Donald is forced to run a long way away, then come steaming back, screaming, into the door, which shatters.
In the end, Huey, Dewey, and Louie collect their treats and Hazel and Beelzebub leave since it is "nearly dawn". After waving goodbye to the ducks, Hazel flies away whilst the Trick or Treat song is reprised over the top. A final shot has a jack-o-lantern seen earlier in the film suddenly appear saying "Boo!" and then grinning.
- Donald Duck (voiced by Clarence Nash)
- Huey, Dewey, and Louie (voiced by Clarence Nash)
- Witch Hazel (voiced by June Foray)
- Beelzebub (voiced by Jimmy MacDonald)
- Jack-o'lantern (voiced by Thurl Ravenscroft)
- Disneyland, episode #3.15: "All About Magic"
- The Mouse Factory, episode #4: "Spooks and Magic"
- The New Mickey Mouse Club, March 21, 1977
- The Wonderful World of Disney, episode #24.5: "Halloween Hall o' Fame"
- Good Morning, Mickey, episode #79
- A Disney Halloween
- The Ink and Paint Club, episode #1.34: "Donald's Nephews"
- The Legend of Sleepy Hollow
- Walt Disney Cartoon Classics: Halloween Haunts
- Mickey's House of Villains
- Walt Disney Cartoon Classics: Donald's Scary Tales / Halloween Haunts
- Mickey's House of Villains
- Walt Disney Treasures: The Chronological Donald, Volume 4
- Walt Disney Gold Classic Collection: The Black Cauldron
- The Black Cauldron: 25th Anniversary Edition
- When Witch Hazel screams near the beginning, it is the same audio used by The Evil Queen when she falls off the cliff in Snow White and the Seven Dwarfs, and later by Maleficent in her dragon form after Prince Phillip throws the Sword of Truth into her heart in Sleeping Beauty.
- A comic book adaptation of the short, written and drawn by Carl Barks, was published in Donald Duck #26. One of the notable additions to the story (and one cut from early printings) was Smorgie, a multi-armed ogre that Hazel summons to try and get candy from Donald.
- When this short was made, it had another opening version that only showed RKO Radio Pictures logo.