After watching a movie, Grim teaches Billy to possess people by jumping into their heads. Billy possesses Mandy and makes her do assorted things like flirting with Irwin, kissing Mandy's mother, going into both men's and women's restrooms and eating earthworms. In the end, Billy leaves Mandy's head, but later that night, Mandy possesses Billy's cat, Milkshakes, to maul him as a form of revenge.

With Irwin not answering the phone, Billy's parents missing and Mandy saying she wants "Billy for dinner", Billy and Grim assume Mandy is a cannibal who ate Billy's parents and friends. Looking for proof, Billy and Grim find tiki figures and arrangements for a celebration in Mandy's backyard. Ultimately, it is revealed that they are just celebrating Billy's birthday. Still, Mandy burps out Irwin's glasses.