Garfield [Frank Welker] lives with dog Odie [Gregg Berger] and owner Jon Arbuckle [Wally Wingert] in a world where comic and cartoon characters breathe, work at Comic Studios, and create the strips that appear in books and newspapers. The group includes his girlfriend Arlene [Audrey Wasilewski], frenemy Nermal [Jason Marsden], Billy Bear [Fred Tatasciore], Randy Rabbit [Stephen Stanton], and inventor Wally Stegman with his wife Bonita [Jennifer Darling], all part of a bustling, self-contained universe that feeds into the real world when the comics are published. Garfield is tired of the old jokes his friends crack and longs for something beyond the familiar punchlines of Toon World.
The Garfield Comic Strip requires a bone for Odie, but he resists returning it to the prop boy and tries to hide it. An accident sends the bone through the studio screen, and the toons discover that the screen is the boundary between Toon World and the Real World, with no easy way back. Garfield seizes the chance for a new life and steps through the screen unnoticed, entering the Real World. When the others try to patch the border to prevent access, Eli, the head technician, tapes a barrier to seal the entry, but Odie himself accidentally crosses after the bone, pulling Garfield along as well. Now both are stranded in a world that is bright, unfamiliar, and constantly hungry for new adventures.
In this unfamiliar city, Garfield and Odie must adapt to life outside their animated studio. They quickly run into trouble and, before long, Odie befriends Shecky, an alley cat who dreams of stardom. Shecky, full of grit and charm, explains how strays survive by playing to the people in buildings, often scoring meals by drawing attention and wits. The two dogs also confront danger when Odie is chased by a gang of Chihuahuas who want his bone, and Garfield comes through with a quick decision to grab the bone and sprint through a small tree hole to shake off the pursuers.
Seeking a place to belong, the pair heads to Club Shecky, the rough-and-tumble hangout where the alley cat thrives. There they encounter Sheila, a sharp-tongued feline, and Waldo, a loyal hound dog, as they begin to piece together how to survive in this new world. After a late dinner, Shecky brings them to Hotel Muncie, an abandoned inn that has become a home for a colony of stray pets, and he invites them to join this makeshift family. The warmth of the new shelter is appealing, but the reality of their absence from Toon World soon sinks in.
The next day brings a flood of worry: their absence threatens to cancel Garfield’s strip. An article appears begging readers to try out to replace him, and Garfield and Odie set out to prove they belong, hoping the judges will recognize them as the real deal. The first auditions fail because the judges mistake them for impersonators, and they nearly lose their jobs. A glimmer of hope arrives when the judges reconsider and give them one last chance: if they cannot return home within 24 hours, two muscular rivals will replace them. Garfield hatches a bold plan, recalling Wally’s invention and deciding to build a tunnel that can pass through the screen, hoping to bridge the two worlds once again.
That night, the rivals close in, capturing everyone at Hotel Muncie and setting the place on fire. Billy Bear, Wally, Jon, and the others race through the tunnel, which Wally names the Bonitanator after a blade that reminds him of his wife, in a desperate bid to reach safety. Yet exits are blocked, and the group faces a perilous climb. Shecky discovers a fire-proof trash cart, and they work together to escape as Odie realizes his bone is missing. It turns up resting on a chandelier, and Garfield reaches for Odie’s paw to pull him aboard, but the chandelier begins to fail. In a last-ditch surge, the group is hurled through the tunnel just as it seals, and they are returned to Toon World.
Back in their original home, Garfield and Odie are welcomed as heroes. The world celebrates their return, and Shecky’s star rises as he chooses to stay with the group, finally realizing his dream of making it in show business. The aftermath reveals that Hale and Hardy, the rival duo, now roam the streets on their own, and a few Chihuahuas who hurtled into the real world manage to hide aboard the tunnel, hinting that the adventure may not be entirely finished. The tale closes on a note of reunion and resilience, with Garfield and Odie rediscovering their place in both Toon World and the Real World, united by friendship and a shared appetite for discovery.
