In this animated musical the well-to-do dog Lady is raised by a couple that has a baby, and Lady falls in love with the independent dog Tramp.
Jim Dear gives his Darling a puppy for Christmas, and he makes the dog Lady sleep in a basket the first night. Lady pushes the door open and climbs the stairs, goes into the bedroom, and howls by the bed. Jim picks her up and puts her on the bed. At six in the morning she wakes them up. Lady goes outside, finds a bone, and buries it. She chases a rat and brings in the newspaper. Jim says she is six months old and needs a license.
Darling puts a collar on Lady. The neighbor dog Jock sings “Loch Lomand,” and Lady shows him her new collar. They go to visit the hound Trusty. Jock says Trusty has lost his sense of smell. Jock says she is a full grown lady. Lady hears Jim and beats him home.
By the railroad station Tramp wakes up, drinks water, and looks for food. He goes to Tony’s and is thrown a bone. Tramp hides from the dog catcher, who puts up a notice that unlicensed dogs will be impounded. Tramp opens his wagon and lets the dogs escape. The dog catcher chases him.
Jock and Trusty call on Lady. She says that Jim and Darling are acting strangely and are ignoring her. Lady says that yesterday Darling would not take her for a walk or play with her. Trusty and Jock explain that Darling is expecting a baby. Tramp approaches and joins the conversation. Tramp tells how things will be different. Jock says Tramp has radical ideas and tells him to leave.
Months go by, and women give Darling a shower of presents. On a rainy day Jim learns it is a boy. Lady wonders what a baby is like and sings “What Is a Baby?” Darling holds her baby and sings “La La Lu.”
Jim and Darling are going away for a few days, and Aunt Sarah takes care of the baby and shoos Lady away. Twin Siamese cats come out of a box and sing “The Siamese Cat Song.” They overturn a fish bowl, but Lady saves the fish. Lady barks, and the Siamese cats get sympathy from Aunt Sue. She takes Lady out and buys a muzzle for her. Lady creates mayhem and runs off with the muzzle. Three fierce dogs chase her, and Tramp defends her. After a tough fight, they run off. Tramp sees the muzzle and takes Lady to the zoo. He gets a policeman angry at a man, and they go in. Tramp says the alligator needs a muzzle. They see a beaver working on a log, and Tramp suggests a log-puller and gives him a sales pitch. The beaver wants to try it, and Tramp tells him how to get it off. The beaver uses the muzzle to move a log.
Tramp tells Lady that he has more than one family. He tells her about the Schultze family and the O’Briens. He takes her to Tony’s. Tony and Joe call him Butch and see his new girlfriend. Tony shows them a menu and says they want spaghetti and meatballs. Tony plays an accordion and sings “Bella Notte” as they eat. Tramp lets Lady have the last meatball. They put their footprints in wet cement. Tramp tells her what a dog’s life can be without a leash. Lady asks who would watch over the baby, and he takes her home. On the way he asks her to help chase chickens. He goes in the henhouse and chases them. They run from the gun shots.
Lady gets taken away to the dog pound where several dogs howl sadly. Lady is brought in while they check her license number. Peg befriends her. The other dogs talk about how Tramp never gets caught and how many females he has known. Peg sings “He’s a Tramp.” Lady gets taken home.
Jock and Trusty both intend to propose to Lady and call on her in her dog house. She is about to decline when Tramp arrives with a bone for her, but she turns her back on him. She says she was embarrassed and frightened. He calls her a trick, and she gets jealous of his girlfriends. Tramp leaves sadly, and rats come near Lady. She barks, and Tramp hears her. In the rain she sees a rat go in the house. Tramp arrives, and she sends him into the house to protect the baby from the rat. Tramp goes in the house and fights the rat, knocking things over. Aunt Sue wakes up. Lady is in the house too. Aunt Sue sees the crib overturned and wants to call the pound because of Tramp.
Aunt Sue tells the man taking Tramp to destroy him. Jim and Darling are returning home and see them. Lady barks and leads them to the dead rat. Josh and Trusty see this and go after Tramp. Trusty manages to pick up the scent and leads the way. They catch up to the wagon and disturb the horses. Lady arrives. Josh sees that Trusty was crushed under a wheel.
In the final scene Jim takes a picture of the puppies that look like Lady and Tramp. Jim lets in Josh and injured Trusty. Josh sees that Tramp has a collar and a license.
This Disney cartoon feature suggests that romance is possible between someone with a wealthy life-style and a poor one who likes freedom and has much experience.