Plot
On Christmas Day, "Jim Dear" gives his wife "Darling" an American Cocker Spaniel puppy as a present. The puppy, named Lady, grows up and befriends the neighbors' dogs: elderly Bloodhound Trusty and feisty Scottish Terrier Jacqueline, AKA "Jock".
Meanwhile, a Schnauzer-mix named Tramp roams the streets, stealing food and causing trouble for local dogcatcher Elliot, who has labeled Tramp "vicious" and is intent on catching him. Tramp hides out in Lady's neighborhood. Having been shooed away from Darling's baby shower by Darling's aunt Sarah and not realizing why her owners are neglecting her, Lady mistakes Tramp's voice for Trusty's and confides in him. Tramp deduces that Darling is pregnant, and warns Lady that "when a baby moves in, a dog moves out". Upon discovering Tramp's identity, Lady sends him away and dismisses his claims. After the baby girl Lulu is born, the couple becomes busier than ever and Lady begins to wonder if Tramp was right.
Later, Jim Dear and Darling leave for an extended visit to Jim Dear's sister and ask Aunt Sarah to dog-sit. While Aunt Sarah is upstairs, her two Devon Rex cats demolish the living room and pin the deed on Lady. Aunt Sarah immediately takes Lady to a pet store to fit a muzzle. Frightened, Lady escapes into an alley, and is confronted by vicious street dog Isaac, but Tramp saves her.
The two dogs spend the day around the city, and have spaghetti and meatballs for dinner at Tony's restaurant. Lady confesses she is doubtful whether her owners still want her, and Tramp reveals he once had owners, but was dumped after they had a child. Their conversation is interrupted by Elliot, who accidentally captures Lady instead of Tramp, and takes her to the dog pound. Two dogs named Peg and Bull discuss Tramp's self-serving nature with Lady, causing her to question why he did not save her from Elliot. Jim and Darling find Lady at the pound and bring her home, kicking out Aunt Sara and allowing Lady to bond with Lulu.
Learning that Peg and Bull have been adopted from the pound, and regretful that he could not do more to save Lady from Elliot, Tramp returns to Lady's house. Lady decides her place is with her owners, and Tramp leaves. A rat suddenly enters Lulu's nursery, and Lady starts barking frantically, just as Elliot arrives to warn Jim Dear that he has tracked Tramp to their house. Jim Dear locks Lady in a room, and Lady calls for Tramp, who returns and sneaks inside to the nursery. In the ensuing battle, Tramp is injured, but kills the rat. Lulu, whose crib was knocked over in the struggle, starts to cry loudly. Believing Tramp attacked Lulu, Jim Dear hands Tramp over to Elliot to be euthanized.
After being released, Lady leads Jim Dear and Darling to the dead rat, then sets out with Jock and Trusty to rescue Tramp. Realizing the truth, Jim Dear and Darling follow in their motorcar. Elliot's frightened horses crash his cart when the dogs attack, and Tramp is injured further. Jim Dear and Darling catch up, and adopt Tramp as their own to protect him from Elliot.
The family celebrates Christmas together, and Tramp receives his new collar and license. Outside in the yard, Trusty entertains Dodge and Ollie, two puppies adopted by Jock's owner, with the story of how he helped save "a poor stray with a heart of gold".
