Smart, observant, and all-around-nice-kid called Coop, has a pretty decent set up at home, until his sister, Millie, brings home a box of pure evil - a tiny hairless Kat. This creature of insane malevolence is hell-bent on destroying Coop. The only issue is that it only happens when no one is around to see it! Coop must find a way to prove to the world Kat's evil nature .Coop's Best friend Dennis helps him.
10-year old Coop Burtonburger, discovers his life will never be the same again when his spoiled little sister, Millie, brings home an alien cat, and Coop blows up his collar.
Old Lady Munson lays down the law, where Coop is not to set in her yard! But with the help of a giant water balloon sling, Kat makes sure that Coop crosses the line again and again and again.
Coop and Dennis build a tree fort, where Kat uses it to power-up his collar, because the tree fort is very tall. Kat climbs up to the tree fort, and starts communicating with other "Kats".
Kat accuses Coop of stealing Millie's Greenie girl cookies, so Coop must clear his name, and prove to Dad and Millie that Kat ate the cookies, and that he framed Coop for eating the cookies.
Coop comes up with the perfect plan to get Kat out of the house. Coop convinces Dad that Dad is allergic to Kat and has become too much to handle, but Kat turns the tables on Coop to think that Dad is allergic to Coop.
Chaos ensures when Coop and Kat get glued hand to paw, and Kat programmed the new Mechanizor Warrior robot to destroy Coop, but Kat will also be destroyed. So, Coop and Kat must work together to destroy the Mechanizor Warrior.
When a contest for pets is announced in Bootsville, Coop subscribes Kat, because the winner wins a trip around the world. However, Coop regrets this when he realizes he will be taking the trip with Kat if he wins.
As Coop prepares for a big test, Kat comes up with multiple ways to distract him from studying, which in the end, Kat ironically helps Coop remember the things he should study by trying to destroy Coop, thus having a B+ on the test.
Coop discovers a self-help motivational tape in the House of Swap and turns his life around, until Kat uses the tape to remove Coop's new-found power of perfect positivity. Now it's up to Coop to use the tapes to fight evil Kat with an even more evil Coop.
Coop comes up with a plan to make money for a Captain Blasteroid Helmet cutting Old Lady Munson's lawn; Kat tries to stop Coop and Dennis by making the grass grow.
Coop's and Dennis' fathers' compete on who's the best camper during a family weekend in the woods; Coop and Dennis use their knowledge of the forest to lead Kat into escalating confrontations with nature.
Bootsville's annual parade has a Spaced Out theme this year and Dad wants to advertise the House of Swap with a flying saucer float. When Kat augments the float to use as an actual space ship, he and Coop battle for control, taking a destructive low-level flight through the city streets.
Dad builds an ice palace and rink in the back yard, right over the entrance to Kat's secret kitty food bunker. Can Coop and Dennis take the heat, defending the palace against Kat's icy offensive?
Coop brings home a carrot suspended in a glass of water for a science project and Kat subjects it and all the vegetation in the house to super-fertilizer, turning them into an army of killer plants.
Egyptian artefacts at the museum turn out to be high-tech relics from Kat's world. Can Coop evade his school group and a very nosy security guard long enough to keep Kat from opening a Sarcophagus portal to another world?
When Millie finds a new school friend exactly like her, she starts to ignore Kat. Coop tricks Kat into running away but Kat discovers the "real world" is a much harder place to be in than he thought. When Millie finally goes looking for Kat, Coop does everything he can to sabotage her efforts.
Bootsville hasn't won their annual baseball grudge match with Timber Lake in over forty years, and Coop is determined to change the town's losing ways. It's too bad Kat has discovered his latest invention can control the weather.
Kat tries to get fishy frisky bits, and gets Coop banned from the grocery store, so Kat goes to the grocery store to steal fishy frisky bits, but Coop must stop Kat from stealing.
Coop's and Dennis' fathers encourage them to revive a neighborhood tradition, the 'round the block golf challenge. Coop is determined to win, but since his makeshift golf ball is hiding a miniature power source, Kat is determined to stop him.
The Burtonburgers face friends, neighbors, and each other in a local Fishing Derby. When Coop mistakes Kat's transceiver for a fishing lure, Kat is forced to do some deepwater fishing of his own.
Dad comes to school to shadow the kids on Parents' Day. After Millie puts him though a demeaning Show and Tell display, Kat escapes and takes out his frustration on Coop. But this time Kat's on Coop's turf.
Coop's April fool's day jokes have the entire town not believing a word he says, so how can Coop stop what seems to be a Kat led UFO invasion when everyone assumes it to be Coop's biggest joke yet?
Seeing how freaked out Kat gets by a huge stray dog, Coop adopts it as his pet and bodyguard, but the dog is a lot more responsibility then he thought, especially after Coop's plan backfires, as Kat retrains it to destroy the house.
Kat tries to overcome his fear of snow to give Coop trouble in the deadly Demolition Run tobogganing challenge. However, Millie decides to participate in the race too. Can Coop save Millie before it's too late?
The police and Old Lady Munson catch Coop and his friends waking the neighborhood, but each of them tell very different stories about what they think happened.
Kat struggles to perfect a teleporter to transfer Fishy Frisky Bits, roses, yarn, toy mouse, some tea leaves and chocolate across space to his girlfriend. But when he learns he can teleport himself, no house on the block is safe from the cat food burglar. He also keeps driving Coop crazy, when Coop takes on a whole new 4th dimension.
Kat wants a day off, but Coop and the gang play capture the flag right through to his secret forest oasis. Can they survive a forest filled with Kat traps?
When Old Lady Munson shows an unusual interest in Coop and Dennis favorite show, they become equally obsessed with finding out why she likes it, but then Kat gets involved.
It's time for the annual Bootsville Day festival celebrating the town's founding, but when Kat's alien blood causes mutations in some hungry mosquitoes, Coop finds himself in a real Battle of the Bugs!
Kat's penchant for munching as he works on his secret rocket has him tipping the scales with rolls of flab! Coop is thrilled that Kat is too overweight to attack him, but when Millie and dad enforce a strict regime of dieting and exercise, Coop must find a way to keep Kat fat.
After Coop uses cat whispering to make Kat into his new best friend, (although Mr. Kat was obviously pretending) he becomes a pal to all animals, but when Coop invites his menagerie of buddies home, both Kat and dad discover just how wild the animal kingdom can get.
Coop and Dennis join the school soccer team but Coop would rather show off then use teamwork, Coop discovers he can't handle everything alone when he runs afoul of Kat's killer robot worker drones, but will Dennis forgive, forget, and help his friend fight?
When Kat's listening transmitter becomes lodged in his ear, his hearing becomes super sensitive, now Coop's going to use every noise in the house to torture his enemy, but the ultimate weapon is Millie's voice.
After Kat's latest tantrum almost destroys the house, Dad starts his own extreme renovation, but when Kat adds a few additions of his own, how far will Coop go to get his own game room?
Kat's attempts to hack into Earth computers are given a leg up by Dennis' new universal remote control and satellite dish, Kat throws every remote controlled device on the block at Coop and Dennis as they try to sabotage his neighborhood satellite network.
Coop joins the Bootsville Rocket Club and with a little secret help from Kat, he's soon the star member, but when Coop learns Kat is going to use his rocket to destroy a satellite, the only way Coop can stop him is to destroy his own record breaking flight.
Coop's hopes of a normal Christmas are shattered by the fact that Kat is constantly getting him in trouble; it is revealed that Kat really misses his family back at his home planet. Coop and Millie's grandparents are expected to visit for the Christmas, but many troubles cause them to be late.
Coop's hopes of a normal Christmas are shattered by the fact that Kat is constantly getting him in trouble; it is revealed that Kat really misses his family back at his home planet. Coop and Millie's grandparents are expected to visit for the Christmas, but many troubles cause them to be late.