In July 2, 1911, two days before the Fourth of July, Lady, Tramp, and their four puppies return from a walk in the park. Among them is Scamp, the most wildest and troublesome (the only boy). He and two-year-old Jim Jr. starts playing with Jim Dear's hat. Jim Dear then gives him a bath for his misbehavior, but to his dismay, he jumps out the window to fetch a ball thrown by Jim Jr.. He runs back in with his paws all muddy, and he chases the ball around the living room and makes a mess. This makes Jim Dear furious, and he chains him to a doghouse outside as punishment. Lady and Tramp are unhappy about his behavior, and Lady suggests that Tramp should talk to Scamp to try and calm him down. Tramp goes outside with a bowl of food for him, who refuses to eat. Tramp tries to make him understand that in a family there are rules for the good of them, but he rebels about being a wild dog and an argument ensues between father and son, and Tramp then leaves angered and irritated after giving him a heavy telling-off, saying that he is a part of this family, whether he likes it or not, and until he starts acting like it, he can just get used to being out in the yard every single night. After awhile, he hears and sees a pack of stray dogs who bully a dogcatcher. He briefly meets a dog named Angel, who nuzzles him in appreciation for returning the dogcatcher’s hat to her. He manages to break free from his chain and runs off to find the pack of dogs he saw earlier. He finds Angel in an alley and follows her to the junkyard where he meets the pack of dogs who call themselves the "Junkyard Dogs". Buster, their leader, gives him a test to prove himself worthy to be one.
The test was to steal a tin can from a vicious dog named Reggie. Scamp almost makes it, but Reggie wakes up and chases him. The dogcatcher appears and tries to nab him, but fails, and he instead nabs Angel with his net. Scamp bites it in an attempt to free her. It hits a lamppost and breaks. The dogcatcher hits Reggie with his van and catches him. Angel thanks Scamp for saving her life and Buster is impressed, but decides that he needs another test before he can be an official Junkyard Dog.
The Junkyard Dogs head to the park, where Sparky, a member, tells a highly exaggerated story of Tramp. Buster comes in angrily and clarifies that Tramp did not die heroically, but instead chose to be a house pet with Lady. Buster, after seeing Scamp scratch in the same manner as Tramp did, asks him if he was related, to which he answers no. Buster then threatens him that if he is, he would kill him.
On a railroad track, Scamp talks to himself about his father’s decision to leave the street dog life. He was then interrupted by Angel who question him about his family, She then reveals that she once was a house pet to five different families who gave her away because they either had a baby, moved, or an allergy. She tells him not to mention this to Buster or he will kick her out of the junkyard dogs society. A train appears and they run for their lives across a bridge. Scamp almost makes it but his paw gets stuck in one of the railroad boards, Angel runs to his rescue and they both fall into the river below. Meanwhile, his family and friends are searching for him, and Tramp thinks he ran away because he was too harsh with him, and regrets what he had done.
Scamp and Angel survive and are unharmed, but realize that their friendship has now blossomed into romance. They then had a romantic stroll in a park and had dinner similar to the spaghetti scene in the first film. They wind up on the street where he lives and they encounter his family searching for him. When he avoids them, Angel is annoyed that he would choose living on the streets over a loving family, as she herself had once been a pet.
At a Fourth of July picnic, Buster clues in that Scamp is Tramp's son, and to verify this, he tells him to steal a chicken from his family's picnic. He, determined to prove that he is a Junkyard Dog, steals it, but is chased by his father. Tramp confronts him in an alley and asks him to come home, but Buster then appears and then an argument ensues between him and Tramp. It ends when Scamp snaps at his father and chooses to stay with Buster. Buster is pleased to see Tramp distraught. A saddened Tramp tells Scamp whenever he's had enough of being a Junkyard Dog, he can come home. Buster officially declares him a Junkyard Dog by removing his collar.
While celebrating that he is a member of the Junkyard Dogs, Angel scolds Scamp for leaving his family and reminds him that they love him, Buster then asks him if he wants to be a house dog which he answers no to and, in annoyance, snaps and accidently reveals that Angel wants to be a one to everyone. Buster then kicks her out and she angrily runs off. Scamp realizes his mistake and tries to find her.
Buster, still wishing revenge on Tramp, sets up a trap so that Scamp, without a collar, is caught by the dogcatcher. Alone and scared in the back of the dogcatcher's van, he sees that he has just made a huge mistake and realizes how selfish he has been. Wracked with guilt, he wishes he were home with his family. Angel sees him in the back of the van and goes to get help from his family. Meanwhile, he is placed in a cage with Reggie. Tramp, arriving just in time, manages to fight off Reggie and rescue his son. However, they are confronted by the dogcatcher who is defeated by Angel. While walking home, Scamp apologizes to his father for running away, and Tramp then apologizes to him for being too harsh. In the junkyard, Buster sees that Scamp returned, and after getting back his collar, he traps him under a pile of trash. His members refuse to help him out and leave to find a family of their own. Scamp, Tramp, and Angel return home and are welcomed back by the whole family. Jim Dear and Darling decides to adopt Angel (after being bought over by their dogs' pout) and at the end of the movie, Scamp is shown taking a bath (he wasn't very happy about that) and the collarless dogs can be seen with their newly acquired families and loving homes.
Joanna Romersa, an animation timing director for this film, was a Disney Trainee for the production of the original one, invited by Jeannine and Darrell to work on this film.
- Scamp, or "Whirlwind" by the way Tramp calls him, (Scott Wolf (speaking) and Roger Bart (singing)), is the young protagonist of the film and bears a strong resemblance to his father. He starts out as a frisky, yet stubborn and selfish puppy, but in the end, he returns changed and well-behaved. He is half American Cocker Spaniel from Lady's side of the family. He is the only puppy known to be a mutt. His romantic interest, Angel, calls him Tenderfoot.
- Angel, (Alyssa Milano (speaking) and Susan Egan (singing)), is the deuteragonist, Scamp's sweetheart and a Junkyard Dog who was once the pet of five families before settling with Scamp's. At the end of the film, she is adopted by Jim Dear and Darling.
- Tramp, (Jeff Bennett) , is the father of Scamp, Annette, Danielle, and Colette. He has become accustomed to house life during his time as a pet. He is portrayed as a firm, yet concerned father. Nevertheless, he still has a few "street smarts" to fall back on and some "good howls" left in him.
- Lady, (Jodi Benson), is the mother of Scamp, Annette, Danielle, and Colette and Tramp's mate. Due to her now being a mother of four, most of her naivety from the first film has been replaced with a sense of responsibility.
- Annette, Collette, and Danielle, (Kath Soucie and Debi Derryberry respectively), are Scamp's sisters and greatly resemble their mother. They are polite yet prissy and show no respect for Scamp but to love him due to the fact that he's their brother. However, their actual names are not mentioned in the film except in the middle of the ending credits.
- Jim Dear and Darling, (Nick Jameson and Barbara Goodson respectively), are the owners of Lady, Tramp, and their puppies.
- Jim Jr., (Andrew McDonough), is Jim Dear and Darling's son and the owner of Lady, Tramp, and their puppies.
- Aunt Sarah, (Tress MacNeille), is the aunt of Jim Dear and the owner of Si and Am.
- Si and Am, (Mary Kay Bergman and Tress MacNeille respectively), are Aunt Sarah's Siamese cats. They have a much more minor appearance in this film than in the first one.
- Jock and Trusty, (Jeff Bennett), are neighbors of Lady and Tramp. When Scamp disappears, they join the search to find him.
- The Dogcatcher (Jeff Bennett) in a style reminiscent of Don Knotts's portrayal of Barney Fife on The Andy Griffith, chases after the junkyard dogs, determined to capture them.
- Tony, (Jim Cummings), is the waiter of Tony's Restaurant.
- Joe, (Michael Gough), is Tony's assistant. Both have only minor appearances in this film.
- Junkyard Dogs
- Buster (Chazz Palminteri (speaking) and Jess Harnell (singing)), is a rottweiler/doberman pinscher mix, leader of the Junkyard Dogs and the main antagonist of the film. He used to be the protegé of Tramp and was angered that he left to become a house pet with Lady.
- Ruby, (Cathy Moriarty), is an Afghan Hound mix and greatly resembles Balto's Sylvie.
- Scratchy (Dee Bradley Baker) is a mongrel plagued by fleas.
- Sparky, (Mickey Rooney), is a mongrel. He used to know Tramp, and tells a colorful but untrue tale of how he came to leave the Junkyard Dogs.
- Francois, (Bronson Pinchot), is a French Bulldog.
- Mooch, (Bill Fagerbakke), is an old English Sheepdog. He is fairly dim-witted but enthusiastic.
- Otis, (Rob Paulsen), is a Chinese Crested. He's very mad and dirty.
- Reggie (Frank Welker) is the mute secondary antagonist of the film. He is a stray bulldog/pitbull mix.
The film was released on VHS and DVD in February 27, 2001, and was re-released again on DVD in June 20, 2006 along with Lady and the Tramp: Platinum Edition DVD.
It was re-released again this year as a Special Edition for the first time in high definition on Blu-ray on August 21, 2012.
- Welcome Home - performed by the chorus, Jeff Bennett, Jodi Benson, Kath Soucie, Jim Cummings, Michael Gough, and Debi Derryberry. This song is the opening one for the film. It sets up the theme for the entire film - independence. The sequence ends with a Broadway-style performance of various people out in a street singing and waving.
- World Without Fences - performed by Roger Bart. It illustrates Scamp's desire to become a "wild dog" free from boundaries and responsibilities. He is chained to a doghouse in the backyard. He runs around, pretending that he is not and is instead running through the countryside with the Junkyard Dogs.
- Junkyard Society Rag - performed by Jess Harnell, Cathy Moriarty, Bill Fagerbakke, Bronson Pinchot, and Mickey Rooney. Buster sings about the junkyard in which the Junkyard Dogs make their home and about their life, with the others also offering their opinions. The sequence features them traveling through the junkyard and interacting with their surroundings.
- I Didn't Know That I Could Feel This Way - performed by Roger Bart and Susan Egan. This is the love song of the film, showing the blossoming romance between Scamp and Angel. It features them walking through the same park that Lady and Tramp walked through in the first film. At the end, a scene similar to the spaghetti scene from it occurs, but with Scamp and Angel guzzling it down instead.
- If I Can't Have Your Love - performed by Richie Sambora. Scamp realizes the importance of family and how much he misses his home. Lady and Tramp's grief over his disappearance and Angel's want for a family is highlighted.
- Bella Notte (This is the Night) - This is a duet performed by Joy Enriquez and Carlos Ponce. It's an updated pop music arrangement of the song from the first film which is played during the ending credits. The original 1955 song was by Sonny Burke and Peggy Lee and arranged by Robbie Buchanan.
- This is the second Disney movie to have Roger Bart and Susan Egan as the singing voices of the love interests, the first one being Hercules. Bart is the singing voice of Scamp and Hercules and Egan is the singing voice of Angel and Megara. The differences are they sing together in this film but don't in Hercules, and Egan is the speaking and singing voice of Meg.
- Two of the actors in this film previous worked on Ariel from The Little Mermaid. Jodi Benson, the voice of Lady, was the original voice of Ariel and Alyssa Milano, the voice of Angel, served as a model reference for the creation and design for Ariel.
- The dogcatcher's wagon that injured Trusty in the first film is seen on top of one of the trash piles in the junkyard.
- Despite the 1998 VHS release of the first film, it was supposed to be released in 2000, but it was pushed to February 27, 2001.