Lady is the pampered female dog belonging to Jim Dear and Darling. When her human masters bring a baby into the house, Lady feels she's being eased out; and when Darling's insufferable Aunt Sarah introduces her nasty twin Siamese cats into the fold, Lady is certain that she's no longer welcome. The cats wreak all manner of havoc, for which Lady is blamed. After the poor dog is fitted with a muzzle, Lady escapes from the house, only to run across the path of the Tramp, a raffish male dog from the "wrong" side of town. The Tramp helps Lady remove her muzzle, then takes her out on a night on the town, culminating in a romantic spaghetti dinner, courtesy of a pair of dog-loving Italian waiters. After their idyllic evening together, Lady decides that it's her duty to protect Darling's baby from those duplicitous Siamese felines. On her way home, Lady is captured and thrown in the dog pound. Here she learns from a loose-living mutt named Peg that The Tramp is a canine rake. Disillusioned, Lady is more than happy to be returned to her humans, even though it means that she'll be chained up at the insistence of Aunt Sarah. Tramp comes into Lady's yard to apologize, but she wants no part of him. Suddenly, a huge, vicious rat breaks into the house, threatening the baby. Lady breaks loose, and together with Tramp, runs into the house to protect the infant. When the dust settles, it appears to Aunt Sarah that Tramp has tried to attack the child. That's when Lady's faithful friends Jock the bloodhound and Trusty the scottie swing into action, rescuing Tramp from the dogcatcher. Once Jim Dear and Darling are convinced that Tramp is a hero, he is invited to stay...and come next Christmas, there's a whole flock of little Ladies and Tramps gathered around the family.