Grim's refusal to help Mandy win a karate tournament, and the $50,000 prize it promises to the winner, leads her to a curio shop, where the shopkeeper, Kuan Ti, gives her an ancient "Chicken Ball" which, when eaten, allows her to become a great fighter. Mandy easily wins the tournament and does not care about the money anymore, only about fighting. It turns out Kuan Ti is actually Eris in disguise, and this was just another of her schemes to create chaos. Seeing how he has a chance to get rid of the kids and finally be free, he tries to take advantage over this by making Billy a superb fighter too, so he and Mandy can fight ferociously to the death until the entire arena is destroyed. With both still alive, Mandy still demands the prize money, which she uses to buy Hector Con Carne's Bunny Island.

Thinking that the world is chaotic enough as it is, Eris, the goddess of chaos, decides to quit chaos to work at a hamburger restaurant. She entrusts Grim the Apple of Discord to watch over for her, which he seals in his old trunk. The apple frees itself from the chest and goes to Billy. Mandy is attracted by the apple's powers, and after being persuaded by Billy's talking burrito, Billy, Mandy and Grim battle for control of the apple, which divides in three pieces. The battle results in them being fused together into an amorphous mass, and, with an evil grin on her face, Eris decides to offer the apple to Irwin too.

When Billy's parents leave for their second honeymoon, Billy is left alone at the worst possible moment, since he has invited Principal Goodvibes over to dinner so he can recommend him into Rollington Academy for the Gifted. Billy's dad suggest Billy to use Eris, the goddess of chaos, and Hoss Delgado, spectral exterminator, as his substitute parents during the dinner. The dinner is a disaster with Delgado terrorizing Goodvibes, and Eris unleashing giant alien zombie lobsters. Goodvibes forcefully recommends Billy into Rollington Academy, which, as it turns out, is actually a military school.

When Mandy and Grim go to the warehouse store, Mandy notices that everything seems to be in order, lacking any presence of chaos. Hoss Delgado, spectral exterminator, arrives saying that everything has been that way since he started dating Eris, the goddess of chaos. Mandy assures Delgado he must break up with Eris to restore chaos, but fearing her temper, he is reluctant to do so. After failed attempts by Grim, Mandy, Billy, and Irwin to break their relationship, Delgado finally tells Eris the truth about he wanting to break up, and she complies by turning into a giant insect and devouring him.