Jack is tired of the weak, useless toxins in the insecticide, so he decides to enhance it by using his new chemistry set. The result is... a gas that has the ability to clone the subject it was used on.
During Christmas, Oggy and Jack are opening up their presents. Jack receives a new science kit, to his excitement while Oggy receives a new canister of insecticide and a box of chocolates. Dee Dee, however, immediately steals it prompting a chase. The Cockroaches manage to win, causing Jack to try out the new insecticide. Unfortunately the insecticide proves to be a dud.
Jack, having enough of the Cockroaches, decides to experiment with his new science equipment to make a more useful, deadly version of the insecticide. Jack uses Joey as the guinea pig for his new spray. To his horror, Joey sprouts a large tumor from his body which eventually separates and creates an identical copy of himself. The multiple Joeys, along with Marky and Dee Dee begin to chase him. Then, as the cloned cockroaches beat up Jack, Oggy uses the spray on them again, unaware of the effects. This causes an even larger army of Cockroaches to sprout. Oggy runs away in terror, dropping the spray by mistake which one of the Joeys takes.
In the kitchen, the multiple cloned roaches abuse the spray to steal food. The cat duo formulates a new plan. The Cockroaches happily indulge themselves with the contents of the fridge until they notice Oggy and Jack wearing raincoats, properly prepared to stop the army of clones. This results in a massive curb-stomp battle ending in the cats' favor. However, there is one last Joey that needs to be caught, who steals the cloning spray and rapidly fires it at the captured cockroaches.
This results in the house being flooded with cloned roaches. As they evilly laugh away, they once again notice something: the cloning spray has affected the cat duo as well, creating an even larger army of Oggys and Jacks. The cats begin to beat up the Cockroaches, now finally having the upper hand.