The story starts off in Fernfield on Halloween night in 1937, where the townspeople storms to the mansion where Warwick the Warlock has gathered the ingredients in order to summon the Halloween Hound. The ingredients follow: his spell book, his staff and five souls of puppies with the same blood. In the mob, a young boy named Joseph Johnston owns Pip, one of the puppies, who has been stolen by Warwick alongside with his siblings. When the Halloween Hound sucks out Pip's soul, the spell is uncompleted as the sun has rose, so Pip's soul is left to float about the house leaving his body stone empty. Warwick is nearly arrested, but he dives through a mirror swearing revenge. Joseph takes Pip's stone body while his father takes Warwick's spell book. The Sheriff takes Warwick's staff and announces to the townspeople that he would board up Warwick's house to prevent anything else from happening.
The scene then moves 74 years later in the present Fernfield where the protagonists, the Buddies, are on a field trip to Warwick's mansion with their owners, Alice, Billy, Pete, Sam, and Bartleby. When the class go to the graveyard to see Pip's memorial stone, Billy finds himself scared of the appearance of the gravedigger, Mr. Johnston. Overhearing that the legend says that if you say "Halloween Hound" three times in front of Warwick's portal/mirror, you would release the Halloween Hound, B-Dawg, who is a "scaredy cat" tries to overcome his fear by doing the legend. Pip's ghost tries to warn the Buddies, but B-Dawg is terrified by him and accidentally completes the reciting. Billy hasn't come up with his Halloween projects and decides to do Warwick With the help of Sheriff Dan, he borrows Warwick's evidence file and staff. His mother, Janice, buys him his costume for trick or treating which is a A Christmas Story-esque bunny suit, having had misheard him saying, "Hip Hop Rabbit," when he meant "Hip Hop Rapper." He goes as Warwick and humiliates B-dawg in the bunny suit. He meets up with his friends and the Buddies and they go trick or treating.
Two punks, Rodney and Skip, who had scared the class earlier on during the trip go to the mansion to explore. They witness the release of Warwick and the Halloween Hound and Warwick who step out of the mirror. Warwick thinking that Rodney and Skip released them turns them into mice after accusing them of stealing his staff. Warwick learns from his owl assistant, Hoot, that his staff is in the hands of Billy. He immediately sets off to search for it and his spell book. When he and the Halloween Hound leave the mansion, Pip can also leave too. He goes to search for the Buddies. The kids' teacher, Mrs. Carroll and her husband, Mr. Carroll, dress up as Mr. and Mrs. Frankendude. Warwick is petrified by all the kids in their Halloween costumes and Pip disguises himself as a child ghost so he can move around more easily. The Buddies get terrified of him and causing them to get separated from their owners, but Pip is determined to convince the Buddies of the Halloween Hound and continues to pursue them.
The kids come across a house which Billy recognizes from a photo from Warwick's criminal files. Billy realizes that the house belongs to the Johnstons. When Mr. Johnston tries to warn Billy and the kids about the staff, but Billy is terrified and runs off. Meanwhile, the Buddies seek help from a gypsy puppy named Zelda but Pip finds them. He convinces them to help him get back in his body. Zelda tells him that if he doesn't do so by sunrise, he would a ghost forever. He, Zelda, and the Buddies go to Deputy Sniffer, Sheriff Dan's dog, for help, only to be found by the Halloween Hound. While they escape Sniffer confronts the Halloween Hound, only to have his soul sucked out. Warwick finally confronts the kids and demands Billy to give him back his staff, and he unintentionally releases magic from it knocking Warwick into a coffin. The kids escape as he starts pursuing them.
Pip, Zelda, and the Buddies arrive at the graveyard where they find Pip's body as a monument. Zelda starts chanting the spell to return him to it which successfully works. He, now as a normal dog again, thanks the Buddies and runs off to celebrate. The Halloween Hound suddenly appears behind Zelda and the Buddies. Like Sniffer, Zelda confronts him and her soul is also sucked out. He then holds the Buddies hostage by taking them back to Warwick's mansion. Warwick uses Mr. Carroll to get his staff back but he ends up getting into the Halloween party where the costume competition is being held and wins. When Billy tries to convince Sheriff Dan that Warwick and the Halloween Hound have been released, Warwick interrupts by finally getting his staff back. He turns Sheriff Dan into a monkey which everyone thinks it's a magic act. The kids try to escape, but are cornered by Warwick who believes that they have his spell book. They are saved by Mr. Johnston who knocks Warwick out with his shovel. He takes them to a chapel saying that dark magic can't enter.
Warwick pursues the kids and Mr. Johnston and threatens the former for the spell book using the Buddies. The Buddies are locked up in a cage with Hoot guarding them. Pip returns to the mansion and persuades Hoot that he can change and to free the Buddies. Hoot unlocks the cage and lets them escape. The Halloween Hound returns and seeing Hoot's betrayal sucks his soul out as punishment. The Buddies and Pip are cornered by the Halloween Hound. Pip willingly sacrifices himself by telling the Halloween Hound that he took his siblings' souls and he was the only one left to complete the spell. The Halloween Hound sucks his soul out. Rodney and Skip help the Buddies escape by opening a secret panel behind the fireplace which they run through. The Halloween Hound then goes to open the portal saying, "I'm not waiting for that idiotic Warwick any longer." It is opened and everyone in Fernfield falls under control.
Mr. Johnston and the kids return to the mansion with the spell book. Warwick uses his magic to paralyze Mr. Johnston and takes it back, only to realize that it is actually the Bible. The Buddies hide in the kitchen where Budderball starts devouring pickled eyeballs. The Halloween Hound finds them and B-Dawg comes up with a plan. Just when the Halloween Hound is about to suck Budderball's soul out, B-dawg signals him who farts, releasing out gas, repelling the magic and causing the Halloween Hound to have his own soul sucked out. The kids and Mr. Johnston find Warwick paralyzed after opening the Bible and Billy takes his staff. Billy chants the reversing spell and manages to complete it just as the sun rises. Warwick tries to take Billy with him into the mirror, but Mr. Johnston grabs him and shoves him into it. When Alice worries about his return, Mr. Johnston takes the staff and breaks the jewel entwined in it. The mirror shatters to prevent Warwick from returning. Sniffer, Zelda, Hoot, Pip and his siblings' souls return to their bodies. Sheriff Dan, Rodney, and Skip are turned back into humans while the townspeople return to normal having no memory of being under control.
Mr. Johnston is reunited with Pip as well as the kids being reunited with the Buddies. The kids bid goodbye to Mr. Johnston who has located Pip's siblings' owners and travels around America to return them. The Buddies bid farewell to Pip who thanks them for helping him defeat Warwick. The film ends with the kids waving goodbye to Mr. Johnston as he drives off with the caravan and the Buddies.
- Harland Williams as Warwick the Warlock
- Rance Howard as Joseph Johnston
- Pat Finn as Mr. Carroll
- Jennifer Elise Cox as Mrs. Carroll
- Michael Teigen as Sheriff Dan
- Elisa Donovan as Janice
- Sierra McCormick as Alice
- Skyler Gisondo as Billy
- Sage Ryan as Pete
- Jake Johnson as Sam
- Tucker Albrizzi as Bartleby Livingston
- Max Charles as Joseph
- Skyler Gisondo as B-Dawg
- Charles Henry Wyson as Buddha
- Josh Flitter as Budderball
- Ty Panitz as MudBud
- Genevieve Hannelius as RoseBud
- Frankie Jonas as Pip, a Beagle puppy
- Debra Jo Rupp as Zelda, a Chinese Crested
- Diedrich Bader as the Halloween Hound, an English Mastiff and the secondary antagonist
- Ryan Stiles as Hoot, a Great Horned Owl
- Tim Conway as Deputy Sniffer