It's Halloween but Junie B is afraid to go trick or treating because of the monsters and witches and all other scary secrets Paulie Allen told her. But then she comes up with the scariest costume after all to scare away all the monsters and witches.
Junie B is worried about Halloween all cause Paulie Allen Puffer told her five scary secrets. May spills the beans about it. At home Grandma Miller tells her that her mother will be taking her to get her costume. Junie B is even more worried. She plans to dress up as Squirty the clown to scare away the monsters and witches.
At the costume shop, she is unable to find the exact costume apparel Squirty had, so her mom tells her she'll just have to make up a clown to dress as. Her new clown name is Screamy and he scares everybody, not just the monsters. However while she trick-or-treats, nobody is scared of her and her costume and this annoys her. Also, everyone likes Ollie's cow costume and they're too obsessed with his cuteness to care about Junie B and give her decent candy.
After a trick-or-treat with nobody getting scared, Junie B. is annoyed and goes to sleep angrily, despite the fact that she faced her fear of Halloween. Her dad walks into her bedroom at night and freaks out because he didn't realize that Junie B. still had her clown makeup on. Her mom tells her to wash it off because she really could have scared him to death, but he laughs it off and Junie B. is happy that her clown appearance actually scared somebody.