Plot
While moving to a new home in Boston, a tabby cat is been left behind by his owners. Abandoned, he looks for a refuge. After various obstacles and near accidents, he comes to an old house with fame for being cursed or haunted in the neighborhood. As he enters, he meets the house's owner, Mr. Lawrence, a kindly old magician, and his pets and automations, along with a small mouse named Maggie, her grumpy rabbit friend named Jack, and an electrical bulb-headed robot named Edison. Later, the magician's materialist real estate agent nephew, Daniel, drops by for a visit. Afterward, while Lawrence dozes off, Jack and Maggie locate the cat after he accidentally re-activates Edison and Jack pursues the kitten. Before Jack can throw him out again, Lawrence decides to adopt him, naming him Thunder (after his fear of lightning).
Thunder learns more about the house, as well as the romantic pigeon pair named Carlo and Carla. Meanwhile, Jack and Maggie try in all ways to exile Thunder from the house, jealous and afraid of being substituted. The next day, refusing to be left behind, Thunder is incorporated into the "rabbit out of a hat" routine in the magic show performed for some children at a hospital, to much fanfare. Whilst returning home, Lawrence suffers an accident and is sent to the hospital, as Thunder is left sprawled behind.
With Lawrence in the hospital with a broken leg, his nephew Daniel takes advantage by tricking his uncle to sign over power of attorney, in the hopes of putting his house up for sale. Suspicious of Daniel's intentions, Thunder alerts Lawrence's automatons. When Daniel returns to his uncle's magic trunk home, he brings along two possible buyers for the property. Desperate, Thunder gets Carlo and Carla to attempt to deter and prevent the house from being sold. Meanwhile, once out of the trunk, Jack (who broke his leg in the accident) and Maggie convince the automatons (except Edison) of Thunder's guilt in causing the accident despite Thunder trying to tell the truth. He hopes Carlo and Carla will prove his innocence, which fails when they are intimidated by Jack. Nevertheless, Thunder manages to convince everyone that they need him to save the house since Daniel is proven to be severely allergic to cats. They allow him to stay but lock him in a birdcage. The next possible buyer, a Chihuahua's owner, is also driven away but not before the Chihuahua can rescue Thunder. In a misunderstanding, Daniel is assumed to be harming her dog, whilst attempting to trap the cat. Later, Thunder visits Lawrence at the hospital and is pleased to discover Lawrence never blamed him after all. Thunder returns home and the inhabitants of the house have meanwhile driven two more buyers away believing the house to be haunted.
When Lawrence rushes back from the hospital with the help of some of the children he met there and finds his nephew swinging a wrecking ball, he finally discovers Daniel's true colors. Thunder attempts to save all the automatons from getting crushed, and when he saves Maggie's life, Thunder finally earns the mouse's respect and friendship. They band together and are able to subdue Daniel. Thunder is finally accepted as a member of the family by Jack and Maggie. When Lawrence recovers from his injuries, he returns to entertaining children with his magic shows, in which Thunder now has his starring part alongside Jack and Maggie. Thunder is finally happy to have a family that appreciates him and his Chihuahua friend seeing them all having so much fun attempts to get himself "an audition" to get recruited as part of the team.
