After Al and Pete fail to catch Garfield and Odie, Mr. Cannell hires a giant robot named T3000 to catch any stray animals, including Garfield and Odie.
Garfield and Odie steal bananas and sausages from a store. Al and Pete spot the mayhem and chase after them. Garfield and Odie lead them into an alley that their truck cannot fit through; the two pets taunt them before running away.
Mr. Cannell then fires Al and Pete, introducing them to their replacement: T3000, a robot designed to capture pets violating the law. T3000 then heads out and captures numerous pets before tracking down Garfield and Odie.
Garfield and Odie are watching TV when Harry knocks on the front door. Harry warns Garfield about the T3000, who has replaced Al and Pete. T3000 then barges into the house, sticking Jon to the wall with pink goop. Unable to find any animals in the house, T3000 goes into the backyard, where Harry, Garfield, and Odie are hiding in a trash can. T3000 uses holographic lasagna as bait, which works.
While Harry escapes, Garfield and Odie flee to the park, where T3000 captures Nermal for standing in a restricted area. When Garfield and Odie encounter Al and Pete, they form a truce and devise a plan to defeat T3000.
Garfield and Odie sneak into Mr. Cannell's room to lure T3000 there. T3000 then shows up, damaging much of the room whilst going after the pets. T3000 sticks Mr. Cannell to the back of his bed with pink goop. It then shoots more pink splats around the room, one of which destroys Mr. Cannell's China vase. Garfield takes a violin and smacks one projectile back, hitting a loudspeaker.
Eventually, T3000 suffers from an overload and shuts down. Al and Pete "catch" Garfield and Odie, which gets them their jobs back, as well as a raise. The truce then ends. T3000 is turned into an ice cream vendor; although appearing to be friendly, it vows to be "back" one day.