This section contains plot details about an episode.
It's Halloween on Harvey Street, and the kids are all having a Halloween party in the park. Audrey is a combination of a vampire, a ghost, a werewolf, and a zombie, Dot is Marie Curie, and Lotta is a bunny. Lucretia is dressed as Audrey with two cardboard dummies of Dot and Lotta, which is the scariest thing they've seen so far. Frufru arrives and sees that she's not the only one who came as a rabbit, as she thinks Lotta copied her costume. Lotta made her bunny costume while Frufru bought hers. Soon enough, the sun sets and Lotta heads for home not wanting to do any of the holiday's nighttime traditions. Dot and Audrey tell her that there's so much fun to have on Halloween night, the best being trick-or-treating, which Lotta is terrified off. Nonetheless, her friends will do what they can to help her overcome it. Before they head out, Frufru tells them to go to the Forever Mud Puddle and chant "Muddy Barry" three times.
The girls go to the puddle and chant "Muddy Barry" three times and at first think nothing happened unbeknownst to them, something touched them from behind. The legend states that if you are marked with mud, you will be Muddy Barry's next victim. Bobby arrives dressed as an angel to tell them the legend of Barry, where he fell into a mud puddle and turned into a mud monster, dragging in kids who he would claim as their victims. The only way to prevent him from dragging in the Harvey Girls is if they gather 32 pieces of candy they get from trick-or-treating before the night is over.
Lotta, too afraid to go through with the traditional method, suggests they use their secret chocolate stash to substitute it, hoping Barry won't know the difference...until they find out that their chocolate has been half-eaten (thanks to Audrey trying to eat a chocolate sandwich). They mold it up into candy with wrappers and take it to the puddle. At first, they seem to be in the clear as Barry gave a sign that it was accepted. But just as Lotta is ready to call it a night, Audrey and Dot disappear, leaving her alone. Bobby reminds her that the candy needed to be from trick-or-treating. Now, Lotta has to face her fears and get 32 pieces before the night is over. But she is not convinced until hiding in her room proves to be a bad idea since she named all her rabbits after her friends.
Lotta begins her trick-or-treating experience and soon gets treats from all the kids on the block, not at all getting tricked once. Soon enough, she gets 32 pieces and takes it back to the puddle where she finds Audrey and Dot trapped inside a pumpkin like a cage. Suddenly, a mud creature rises from the puddle and takes the candy, but it also prepares to send Audrey and Dot to their muddy doom. Determined to save her friends, Lotta sprays the mud creature with a hose and washes the mud away.
The creature reveals to have been Frufru trying to get back at Lotta for having a bunny costume like her. As she leaves, a boy named Barry Mudderson (who was rumored to have been Muddy Barry) arrives and frees Audrey and Dot. Lotta tells them how much fun she had trick-or-treating, but her friends would like to call it a night. Just as they leave, Barry falls into the mud puddle again.