In a charming town set around the year 1909, Jim Dear surprises his wife, Darling, with a delightful cocker spaniel puppy named Lady as a Christmas present. As Lady flourishes under the tender care of her devoted owners, she forms a close friendship with her next-door neighbors, Jock the dashing Scottie and Trusty the wise, elderly Bloodhound.
Simultaneously, across town, a streetwise terrier mix named Tramp navigates life by scavenging for food and relying on the kindness of strangers. He orchestrates a daring escape for his friends, Peg, a feisty Pekingese, and Bull, a tough Bulldog, from the clutches of a relentless dogcatcher. While evading capture, Tramp stumbles into Lady's neighborhood, where he overhears her expressing concerns about her owners' growing detachment due to the impending arrival of a baby. In an attempt to share his valuable life experience, Tramp warns Lady that > "when a baby moves in, a dog moves out." His unsolicited counsel, however, irritates Jock, who swiftly drives Tramp away.
Despite Jock's dismissal, Tramp's ominous advice lingers in Lady's thoughts, causing her distress as Darling's pregnancy progresses. When the baby finally arrives, Lady finds comfort in her budding bond with her new sibling, dispelling her earlier fears.
As time passes, Jim Dear and Darling decide to take a short trip, entrusting Lady and their newborn to the care of Jim Dear's strict Aunt Sarah. Disapproving of dogs, Sarah prohibits Lady from nearing the baby, and chaos ensues as her mischievous Siamese cats, Si and Am, create turmoil in the household. In a crafty act, the cats fabricate a false attack, blaming Lady and prompting Sarah to fit her with a muzzle.
In utter panic, Lady escapes into the streets, chased by a pack of wild dogs until Tramp comes to her rescue. He brings her to a nearby zoo, where a friendly beaver removes her muzzle. In a whirlwind of adventure, Tramp introduces Lady to his carefree lifestyle, culminating in a romantic spaghetti dinner at Tony's Restaurant, followed by a leisurely stroll through the park.
The next morning, Tramp tries to persuade Lady to join him in a world free from ownership but, despite her newfound feelings for him, Lady remains committed to her responsibility of watching over the baby. As they head back from their escapade, Tramp's antics attract the dogcatcher, who captures only Lady, sending her to the local pound.
At the pound, Lady reconnects with her friends Peg and Bull, alongside other strays who all know Tramp. They share tales of his romantic adventures, shedding light on his many conquests. When Sarah arrives to punish Lady for her misbehavior, she confines her in the backyard. Jock and Trusty suggest a whimsical solution: marrying one of them to escape the oppressive household. Lady, however, graciously declines their proposals, determined to maintain her independence. When Tramp returns, apologizing for his past actions, Lady, upset by his history with other dogs, firmly tells him to leave.
Suddenly, Lady's instincts kick in as she notices a suspicious rat sneaking into the baby's nursery. Despite her attempts to alert Sarah, they go unheard. Yet, Tramp hears Lady's urgent barking and rushes back to save the infant from the rat's threat. Although Tramp gets injured during the confrontation, he manages to eliminate the rodent, while Lady escapes her chains to assist him. Soon after, the baby's crib falls, triggering a frantic reaction from Sarah, who believes the dogs have attacked the child.
When Jim Dear and Darling return, they find Lady locked in the cellar and Tramp facing the dogcatcher. Skeptical of Sarah's fabricated story, Jim Dear releases Lady, who reveals the slain rat as proof of their innocence. Realizing the truth, Jock and Trusty rush to save Tramp, but a melee ensues, leading to a serious injury for Trusty during the chaos.
As the seasons change and Christmas approaches, Tramp has found his place within the family. Together, he and Lady have welcomed four adorable puppies, receiving a visit from Jock and a recovering Trusty. As the pups listen eagerly, Trusty attempts to regale them with his well-worn tales, though he amusingly struggles to remember them, bringing joy to the entire family.
