When Garfield unexpectedly receives a helmet that reads a person's mind, he finds two aliens planning to take over Earth.
Herman Post arrives at the Arbuckle house with a large package. Just as he’s about to press the doorbell, Garfield sends him away with a skateboard. Garfield is initially satisfied with the package, expecting it to contain a waffle machine he ordered, but then finds a telepathic helmet instead. Despite his disappointment, he decides to try out the device on Odie. It doesn’t work with the brainless dog, but does work with Jon. With it Garfield discovers that Jon baked him frozen lasagna and has carrot cake hidden in the fridge.
Around the city, he finds several subjects to make further use of the helmet, including Nermal and two suspicious-looking people. He discovers the latter are really aliens, who plot to invade Earth and enslave humankind if Vito’s Pizzeria is considered the best pizza in the universe. Garfield tries to warn Vito, but has no luck due to being banned from his store. The aliens, back in their disguises, enter Vito’s to sample his pizza. Watching through the window, he discovers that the aliens are vulnerable to anchovies.
At nightfall, past closing time, Vito tries to get the aliens to leave. As the aliens consider Vito to have the best pizza in the universe, they bring his store (along with Garfield) to a spaceship. The two-headed alien leader, Emperor Kaal’zone, arrives at the store, expecting to try Vito pizza, with promise of “major interstellar distribution” if he likes it.
Vito is excited about the offer until Garfield gives him the telepathic helmet. Discovering the aliens’ true intentions, Vito (with Garfield’s help) makes a pizza with anchovies. When the emperor gets a taste of the pizza, he accuses the other two aliens of treason, sending them to work mines, and cancels the invasion of Earth, with Vito’s pizza declared the worst of the universe. Back on Earth, Vito makes numerous pizzas for Garfield as a reward for his work.