The Simpsons family tries to watch a Halloween special but keeps getting interrupted.

Homer serves crème brûlée and sends Bart to the shed for butane.

Bart discovers an alien in the shed while looking for butane.

Kodos claims he came in peace and was left behind accidentally.

Lisa offers help and Kodos asks for equipment to phone home.

Kodos secretly tells Lisa to find missile defense locations, then sings about killing humans.

Homer tries to seduce Marge but thinks she has tentacles.

Homer hides Kodos from government agents who come to the house.

Kodos kills the government agents using a space portal.

Bart returns and learns Kodos is evil, but the family watches the dissection.

Homer is assigned to kill reporter Kent Brockman by Mr. Burns.

Homer and Marge each make up fake plans for the night.

Homer and Marge separately try to kill Kent Brockman but fail.

Homer realizes Marge is also a professional assassin.

Homer and Marge fight over their secret assassin careers.

Bart and Lisa interrupt the fight and Homer and Marge pretend everything is fine.

Bart, Nelson, Milhouse, and Lisa go trick-or-treating and get empty-bagged.

The kids decide to trick everyone and start causing chaos.

Ned Flanders asks God to help scare the kids straight.

The kids enter the church's haunted house to be scared.

The kids are shown the seven deadly sins and promise to stop sinning.

The episode ends with a warning that viewers are going to hell.