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Ten-year-old Coop Burtonburger's life takes a turn for the worse when his little sister, Millie, brings home a mysterious stray cat who, in reality, is an evil cybernetic alien in disguise. To make matters worse, neither his family nor anyone else believes him, except for his best friend, Dennis. Now, Coop risks his life every day as he attempts to foil the cat's diabolical schemes and prove to the world that the family pet is an evil mastermind.
Coop falls for Old Lady Munson’s niece Fiona, and Kat does everything he can to make Coop look bad.
When Millie tickles Mr. Kat's 'tickle spot' he goes into a blissful state that renders him useless as an alien agent and when Kat's empire find out about him they send a robot to destroy Millie.
Kat's swarm of flea-sized mind control robots hop into the ears of the people of Bootsville and soon they all destroy Coop.
With Coop out of town, Kat wants to turn water into milk and Dennis comes to the rescue.
Millie brings home the class hamster, unaware that Mr. Kat hates hamsters.
When Kat uses his growth ray to bury Bootsville in a catnip jungle, Coop is blamed by the irate Bootsville Gardening Club.
Coop tries to stop the destruction of Massive Mart.
Kat builds a Rat-ray gun, which he plans on using to turn Coop into a rat, but Dad gets zapped instead, so Coop hopes he can change Dad back... If he can catch him first!
Coop and Dennis climb inside Kat's scratching post and discover Kat's alien technology has created an infinity within.
Coop, Millie, and Dad are taken away to a top secret base to be interrogated, after a UFO investigator suspects they are aliens.
After taking the fall for one too many of Kat's destructive escapades, Coop decides to let Kat have free rein to cause whatever destruction he wants.
Due to an ‘over-loading’ problem on the Kat Nebula, Kat plots to turn Bootsville Beach into a giant litter box.
Kat’s devious magnifier satellite is causing a dangerous heat wave in Bootsville.
Coop and Dennis compete with one another to reduce their carbon footprints.
Coop uses Kat’s time machine to go back to the past and stop Millie from bringing Kat home, but ends up altering the future for the worse.
Coop tries to undo the Kat invasion, which he brought about by fooling with Kat’s time machine.
Coop becomes Dennis’ wing-man for a change, as they go in search of the 'sewer-croc-baby'.
Coop breaks every window in Dennis' house, and is forced to work off his debt by working in Henry's store.
Growler swallows a Kat device which makes him grow to the size of a T-Rex.
Kat's malfunctioning spybot thinks Coop is its new master, and wants to protect him from Kat.
