While Garfield waits for Jon to get more lasagna on his birthday, he is observed by aliens that resemble lasagna.
In the early morning, Jon is asleep before Garfield appears and wakes him up with an alarm clock. Afterward, he reveals it to be his birthday, sending Jon into panic. Arbuckle cooks him eight birthday lasagnas, before leaving to add the footage to his "lasagna home video montage". After consuming them, Garfield notices Jon cooked one less. He alerts the human about the matter, prompting Jon to go to the market as Garfield sleeps, and Odie plays.
Meanwhile, a small spaceship leaves their backyard, and returns to a space station, that resembles an oven. A "space lasagna" named Ricotta returns to the leader of the space station, General Gorgonzola. Gorgonzola shows Ricotta images of Garfield holding lasagna, and requests the latter to find out what happened to them. Ricotta returns to earth, and encounters Odie. He measures the dog's brain capacity, which turns out to be zero and manages to sneak into the house, using a flower.
He sees Garfield, and uses a ketchup bottle and a trashcan to get to the cat's level. He falls into the trashcan and tips it over, waking Garfield. After Ricotta stays motionless on a plate, Garfield sees and assumes him to be the last birthday lasagna. Ricotta speaks out, making Garfield to stop before Ricotta proceeds to beat him up. The lasagna then leaves the house. After Odie returns to house, Garfield explains the situation to the dog, who doesn't believe him. Odie then follows a scent to a bush where Ricotta explains to Gorgonzola that Garfield was easy to defeat, prompting Gorgonzola to begin an invasion.
Odie warns Garfield about the space lasagna, until the lasagna appear in the backyard, making Garfield hide in the garage. The lasagna capture Odie, and begin to search for Garfield. As they search, they find Jon's video compilation, scaring them all. Garfield comes out of the garage, unties Odie and goes to Jon's room. As the lasagna talk over the footage, Garfield appears which scares them off. Garfield then reveals to Odie that he is relieved to see them gone. Jon returns home with the last lasagna, prompting Garfield and Odie to run off. Meanwhile in space, the lasagnas fly off screaming.