When a mysterious stray cat is brought home by Coop's little sister, his idyllic life is turned upside down. Kat is a super-smart, conniving mastermind with a fanatical hate for Coop.

Kat declares war on Coop-to the death; they fight constantly as Coop tries to stop Kat and tell the world about his possible plans. Kat destroys the evidence and puts the blame on Coop every time.