In the outer reaches of the galaxy, a mother ship in the shape of a pressure cooker is home to some very strange creatures: space lasagna! Their ambition is to invade Planet Earth. When the space lasagna check out Jon's neighborhood, they run into Odie. They think that all humans are just like him, and decide to invade.

Hunting birds is something Garfield gave up long ago. It's like eating mice : he just can't do it ! But when he finds a nest full of what look like abandoned eggs, Garfield puts his feline pride to one side and decides to hatch them. Harry, the stray, doesn't agree with this plan; he would love to put the newborn birds right on his dinner menu.

It's Halloween and Garfield has dressed up as Catzilla, a fierce wild cat, to go out trick or treating. He has painted stripes on his fur and added false teeth to complete his disguise. But what he doesn't know is that the real Catzilla has escaped from the zoo, and the neighbors are terrified of running into him. Garfield is busy trick or treating, going from door to door to collect candy.

Odie's nocturnal energy leads to a garden encounter with a Martian; a body-switching thank-you gift leaves Garfield as a dog and Odie as a pampered cat; Garfield despises dog life, prompting their desperate efforts to revert the switch.

Jon has gone out on an errand and Garfield and Odie are home alone with a dish full of spare ribs and instructions not to touch them under any circumstances. But of course Garfield immediately wolfs them down, telling Odie to get lost so he doesn't have to share. In the meantime, Odie finds a bone out in the garden.

Another day has begun, and Jon is doing the housework. He realizes Garfield and Odie are really dirty and disorderly. But Jon has a stroke of luck: a salesman knocks at the door and quickly talks Jon into buying a very efficient cleaning robot. They shake on the deal and Jon puts the robot to the test.