While moving to a new home in Boston, a couple stops the car and the woman opens the door and throws a toy ball on the sidewalk so that their tabby ginger cat can chase after it. The cat, who still seems kittenish, later realizes that he has been abandoned by his owners when they close the door and drive away without him and looks for a refuge. A tiny Chihuahua attempts to befriend him but is quickly dragged off by his leash. After various obstacles and near accidents, he’s chased by a large Doberman until he comes to an old house with fame of being cursed in the neighborhood. Entering via an open attic window, the cat explores all the strange contraptions about and tries to befriend a small mouse named Maggie, who’s terrified of him despite the cat trying to convince her that he doesn’t even eat mice. Soon, he is threatened by Jack, Maggie’s rabbit friend, and Maggie; ordering him to leave the house before their owner sees him, afraid the cat will monopolize his love and attention since he’s a bit of a cat-lover. They throw the cat out but he finds his way back in through a cellar window, attempting to escape a thunderstorm, and explores more of the house. Then, he hides behind an urn as the house’s owner, Mr. Lawrence, a kindly old magician, has a conversation with the various automatons and gizmos he created for his magic shows while fixing one of his own named Edison (after Thomas Edison) and later, his materialist and real estate agent nephew, Daniel. Afterwards, while Lawrence dozes off, Jack and Maggie locate the cat after he re-activates Edison and Jack pursues the kitten but before he even attempts to throw him out, Lawrence wakes up and picks up the kitten and decides to adopt him, naming him Thunder (after hearing thunder strike again).
Thunder learns more about the house, as well as the love birds pigeons named Carlo and Carla. Meanwhile, Jack and Maggie try by all ways to exile Thunder from the house, jealous and afraid of being substituted. The next day, after performing a magic show at a hospital for children and while riding on a bicycle, Jack tries poking Thunder with a crayon in order to get rid of him; hoping he won’t find his way back. However, during the event, Lawrence suffers an accident and is sent to the hospital.