As Haloween approaches, all the kids are excited about what costumes they are going to be wearing. Vinny and Jessie both agree not to go as Space Beasts, but both then break their promise, however while Vinny comes in a proper Space Beast costume, Jessie's home-made version makes him look more like a mermaid. Mr Besser is determined to go as a pirate, but when Vinny and Jessie teach his parrot bad words they both get found out at the party. Meanwhile Nancy finds out that Penny is going as Little Bo Peep and decides to buy the same costume, but when she arrives at the party she can't find Penny, only a person dressed up as a sheep. Assuming that it must be Penny, the two enter the costume contest together, only to find out too late that it is actually Polly inside the costume.