In the heart of Paris, France, the wealthy and aging socialite, Madame Adelaide Bonfamille, resides with her elegant cat, Duchess, and her trio of playful kittens: Berlioz, Toulouse, and Marie. Assisting in her lavish life is the less-than-amiable butler, Edgar.
One fateful day, Madame reaches out to her friend, George Hautecourt, with the important task of finalizing her will. Unbeknownst to them, Edgar is eavesdropping on their conversation. Madame reveals that since she has no living relatives, she considers her beloved cats to be her family and intends to leave her entire fortune to them, with Edgar set to inherit once the cats have passed away.
This revelation sends Edgar into a furor, as he realizes that these cats will likely outlive him! In a desperate attempt to retain his future wealth, he slips sleeping pills into the cats’ cream and, under the cover of night, transports them out to the countryside, plotting to abandon them. However, his plans go awry when two lively dogs, Lafayette and Napoleon, give chase. Edgar soon leaves the hapless cats behind in a field and hastily returns to Paris.
Upon waking, the bewildered cats find themselves far from home and soon encounter a charming alley cat named Thomas O'Malley](/actor/phil-harris). He offers his assistance in their quest to return to Madame Bonfamille. Meanwhile, back at the mansion, a clever house mouse named Rocquefort is conversing with Madame's horse, Frou-Frou, expressing their concern over the missing cats. Edgar waltzes in, blissfully unaware of the havoc he has caused, and naively reveals to Frou-Frou a newspaper article about a mysterious catnapper.
As the mischievous cats embark on their adventure, they hitch a ride on a milk truck, only to be discovered by the driver. They attempt to follow the train tracks but are forced to leap aside when a train passes by, causing little Marie to get swept away in a nearby river. Heroically, O'Malley jumps in after her, and the family must navigate the tumultuous waters together.
Their journey introduces them to two delightful geese, Abigail and Amelia, leading them to their rather tipsy Uncle Waldo, who narrowly escaped becoming dinner in a restaurant. Meanwhile, back in the countryside, Edgar retrieves his forgotten belongings only to find himself once more being chased by the persistent dogs.
In the meantime, O'Malley and the kittens experience a brief respite at the warm abode of Scat Cat and his band of alley cats, where they are treated to unseen antics before departing into the night. A tender moment blossoms between Duchess and O'Malley, as she expresses her longing to be reunited with Madame, while O'Malley, having never known kindness from humans, struggles to understand that the cats are more to Madame than mere pets; they are treated like family.
As dawn breaks, O'Malley leads his newfound friends back to Madame's lavish mansion. However, their joyous return is thwarted when Edgar captures them in a burlap sack. Witnessing this, Rocquefort rushes to O'Malley for help. Once informed, Thomas hurries back to the mansion, seeking the assistance of Scat Cat and his gang.
In an intense standoff at the stables, Edgar locks the cats in a trunk, detailing his plan to send them to Timbuktu. But moments later, a heroic O'Malley bursts in, instigating a brawl, while Scat Cat and friends arrive just in time. With Rocquefort’s cleverness, they successfully liberate the captured cats, while Edgar gets himself locked inside the trunk.
Following this chaos, Madame soon grows concerned over Edgar's sudden disappearance and instructs George to revise her will, excluding Edgar from any inheritance. In a heartwarming conclusion, Thomas is officially welcomed into the family, and Madame decides to convert her grand home into a sanctuary for all the alley cats of Paris. The film culminates in a delightful celebration, as Scat Cat and his crew throw a vibrant party in their newfound haven.
