"Once upon a time..." Prince (Tim Curry), a cat who lives a pampered life in Carlisle Castle, with servants. "Across the pond...we see a cat who thinks he is king". And we see Garfield (voice of Bill Murray), coming inside the house, pointing out all the good things in his life. Jon then practices proposing marriage to Liz's photo, but of course Garfield thinks he is talking to him. When Garfield realizes that Jon is going to propose to Liz, he starts arguing at Jon, saying Liz changed him. Liz (Jennifer Love Hewitt) arrives; she has great news to tell Jon. She was asked by the Carlisle Animal Conservatory to speak in England. Jon is a bit crestfallen but tells her he has his own good news. He can't find the purple velvet box with the ring; Garfield, after eating the turkey, is playing with the box. Jon says the good news is that he got Odie (the dog) toilet trained. Jon gets the idea of following Liz to England.Carlisle Castle. Lady Carlisle died, leaving the estate to Prince. Her nephew of course was expecting to get the estate and is told by the three solicitors that when Prince XII dies, he gets the estates. Now all he gets is 50 pounds a month and being able to continue to live at the castle. There are some barnyard animals outside paying attention to this. Next day Jon gets Garfield and Odie to the kennel. While Jon fills out paperwork, Garfield breaks out, and Odie follows him. They stowaway in Jon's car (a Volvo), and Garfield empties Jon's luggage to make room for him and Odie.Carlisle Castle. Winston the bulldog announces Prince XII to the barnyard animals, who are worried about what will happen to them. The nephew, Dargis (Billy Connolly) , plots Prince's death. Jon arrives to London & Liz walks in, surprised to see Jon. But before they can get farther, the luggage opens, and Garfield and Odie pops out. Liz tells Jon don't let anyone see Garfield, since they weren't quarantined Garfield heads to the bathroom, and assumes the bidet is a kitty-bathtub. Dargis puts Prince into a picnic basket and tosses him into a river. Latter Smithee (Ian Abercrombie), the butler, asks Dargis if he seen Prince. Dargis refuses & sends Smithee to London to pick up some suits.Jon and Liz leave to the British Museum, leaving Garfield and Odie to watch TV. Garfield and Odie escape when the maid comes in and there is montage of them looking around London for Jon. They pass a grate where Prince is trying to open to escape the sewers. Garfield runs into the street and almost gets run-over by a Rolls-Royce. It's Smithee, who thinks Garfield is Prince and picks him up. Garfield yells at Odie to get help.Dargis calls the solicitors to tell them Prince is dead or missing, no doubt dying or running away because Lady Carlisle died. The Solicitors are dubious but agree to meet him on Monday with the papers to sign. Dargis makes plans with a woman, Abby Westminster, to find investors to make Carlisle Castle into a resort, and build condos on the property. Abby asks what will happen to the animals, and Dargis says the ones they don't scare away will be fed to the guest. Prince finally gets out of the sewer. Jon finds him and Odie and takes them both to the hotel. Garfield gets to Carlisle Castle. He enters and finds Winston who assumes he is Prince. Winston gets Garfield to talk to the animals to reassure them, but being clueless about what is going on, Garfield makes a fool of himself. McBunny the rabbit realizes that is not Prince, but everyone decides to pretend, so that they don't get tossed out of the castle.Winston toddies to Garfield and finally convinces Garfield to stay, saying that now that Jon is getting married, he doesn't need him. Dargis sees Garfield and assumes it's Prince. He tries to train a rottweiler, Rommel, to attack Garfield, but the animals outsmart Rommel, getting the dog to attack Dargis. At the hotel, Prince tries to get Odie to help him, but Odie (the only animal who doesn't talk), isn't much help. Jon and Liz go to a pub with Prince, who at first turns his nose up at Lasagna, but once he tastes it goes nuts. Garfield lives it up and drives Smithee into exhaustion getting him meal after meal.Garfield passes by a door and overhears Winston and the macaw talk about him. The macaw calls him a common house-cat and a buffoon. Garfield is sad, and realizes he misses his best friend, Jon. Dargis is again trying to train Rommel to attack Garfield but gets interrupted by Smithee. Dargis tells Smithee to take a holiday, and Smithee packs up. Liz has to go to Carlisle castle, since that is where conference is being held. She drops a guidebook for the castle, which Odie picks up and shows Prince. Prince remembers that he has to get back to Carlisle castle too. Jon sees this and runs after him. Dargis meets Liz, he offers her a painting to the Conservation group, but he asks what would she do for him? Garfield realizes Dargis is hitting on Liz, Jon's girlfriend, and gets Dargis's attention. Dargis chases him and catches him in a bag, but the solicitors show up. He leaves them outside, then drops Garfield in the dungeon.Meanwhile, Prince jumps on a boat, then jumps on a van to get to Carlisle Castle. Jon searches for Garfield (Prince) and finally sits down at a park. Odie pulls out of the garbage a newspaper, showing Jon an article about Prince, which shows a picture of the cat. Jon notices the resemblance and assumes someone must have picked up Garfield, thinking it was Prince. They drive a car to Carlisle castle. Winston helps Garfield escape the dungeon, but Garfield tells Winston what he heard them say about him and decides to leave. Garfield passes by a hole in the hedge at the same time as Prince and there is a bit with them mirroring each other's actions. The animals show up, happy to see Prince. Garfield decides to leave, and Prince finds out that they are about to be eaten. So, Prince says what they have to do is run away, preferably to another castle. Garfield thinks that is a terrible plan.Abby Westminster shows up. Dargis tries to get her into another room, while he tries to sign the papers to make him the owner of the estate. Garfield and Prince show up in his periphery, getting Dargis to chase Prince while keeping Abby and the solicitors from seeing Prince. Smithee is waiting on the side of the road for a bus, when Jon stops and ask him about Carlisle Castle. Jon explains how he thinks Garfield and Prince were confused for the other. The other animals are attacking Dargis also. At one point he still thinks it's just Prince. He gets a crossbow and threatens the solicitors to sign the papers. Abby shows up to tell the solicitors about Dargis plans; seems she was hired by the solicitors to spy on him. The two cats show up, and Jon shows up and gets the crossbow away from Dargis. Unfortunately, Liz shows up and Dargis holds a really old-fashioned gun on her, but the ferret goes up his ruined trousers and does ferret like things to Dargis. Dargis collapses.So Dargis is out for the count, and the police show up to haul him away. So, in the same dining room all this drama happens in, Jon proposes to Liz, but can't find the ring box. Garfield hands him the ring box. Liz agrees to marry Jon. Liz sees Prince and Garfield together and wonders which one is which. Garfield kicks Odie, so they figure out which one is Garfield.