In this episode, Gil and Goby see a very spooky haunted house on their way to preschool and they talk to the snail who lives there. She tells them that there is going to be a haunted house party that night. Gil and Goby go tell the other Guppies and they learn all about Halloween.
The opening begins as Molly tries to say "It's time for Bubble Guppies!" However, Gil interrupts by searching for her and she hides behind the clock with a scary mask. When Gil comes by, still looking she surprises him and he runs away! Then Molly says "It's time for Bubble Guppies"
Goby, Gil, and Bubble Puppy are on their way to school, when they see a haunted house. They decide to take a closer look and are surprised when the door suddenly opens. A snail and a crab, named Igor, with Halloween stuff make their appearance. They tell the two guppies and puppy about the party they're going to have. They are all very excited and when Goby and Gil arrive to school, Gil informs them about what happened and he suddenly spots a ghost, but nobody believes him.
At any rate, Mr. Grouper then discusses things that involve Halloween through a spooky tale about when he was once in a haunted house. Then the pop song plays.
After the song, Oona has a cat that doesn't sound right, so she goes to the pet potions store, run by Deema. Soon they manage to find the right ingredients for the hot pet potion called "meow now" to make the kitty-cat meow again and Mr. Grouper announces that it's time for lunch.
Molly is busy decorating as Gil tries to scare her with a small toy bat. She then, unknowingly, returns the favor, scaring him with a much bigger toy bat! She proceeds to chase him around, trying to tell him that the bat she's holding is not real, as a ghost walks on by, nobody noticing...
The girls, Gil, and Goby are drawing Halloween related things when Nonny, dressed
as a Vampire sneaks up behind Mr. Grouper and ends up startling him! The guppies compliment his costume and Gil sees the ghost again! Soon everyone begins to wonder what costumes they'd like to wear for the haunted house party and soon a dance song begins, after that Mr. Grouper tells everyone to go outside.
Once outside, Oona begins the story segment. Molly is a zombie, a very spooky monster. She becomes scared upon seeing a spooky shadow following her and she runs to the spooky-looking Monster Motel, owned by Deema, to hide. Deema gives her a room and they both enter it after managing to pick the right key for it. Once inside, they wait a few seconds before checking outside to see the spooky shadow has followed them! But they soon learn that the spooky shadow was really a small white mouse that was out trick or treating.
Gil soon tries to scare Molly again while she looks at herself in a mirror, this time by pretending to be a mummy. But he accidentally scares himself when he comes across his reflection in the mirror and runs away!
Everyone heads over to the haunted house party in their costumes and they are greeted by the snail and Igor. They ask the guppies to find a spooky jack-o-lantern for the party potion and soon Gil and Goby manage to quickly find it, while Gil sees the ghost again, return it to the snail, finish the potion and it makes a fashion show suddenly occur! After everyone has gone down the runway, called the Black Cat-walk, the ghost appears on the runway, which shocks everyone. But when it suddenly barks, everyone then becomes highly curious as to whom it may be and Gil pulls up the sheet to see that it's Bubble Puppy!
Molly and Gil really enjoyed the Haunted House Party. Gil thought Bubble Puppy was an actual ghost. But Molly explains to him that there's no such thing as ghost when one appears. Gil tries to warn her, but Molly thinks it's just Bubble Puppy again. But when it turns out it's not him, Molly and Gil are quick to flee the scene!