Since arriving on Earth, the aliens - led by the Bird-Kersees - have viewed Halloween as a threat and have set up a barrier at the gates of Hidden Hills to prevent children dressed in costumes from entering the community. The Weavers, on the other hand, are excited about their first Halloween in the suburbs and want to open the gates of the community to celebrate. They do their best to explain the ritual of trick-or-treating to the aliens. Meanwhile, Marty and Debbie's fears are realized when Amber, Max and Abby reject their family costume plans.