Oliver, an orange kitten, is lost in the streets. He steals some hot dogs from a hot dog vendor with the help of a mongrel named Dodger. Together they are successful, but Dodger runs off, attempting to leave the orphaned feline behind.
Dodger eventually arrives at the barge of his owner, a pickpocket named Fagin, along with his meal, to share with his friends: Tito the Chihuahua, Einstein the Great Dane, Rita the Saluki and Francis (Frankie), the Bulldog. Oliver sneaks into their home, located below the city's docks, and is discovered by the dogs. Fagin, owner of the dogs, comes in and explains that he is running out of time to repay the money he borrowed from Sykes, a shipyard agent and ruthless loan shark. Sykes and his Doberman Pinschers, Roscoe and DeSoto, arrive.
While DeSoto is sniffing around the barge, Roscoe flirts with Rita, and smashes the television. He then goads the protective Einstein to let the angry but tiny Tito attack him, when DeSoto finds Oliver. The terrified kitten scratches DeSoto's nose and both Roscoe and Desoto intend to tear him apart when the dog gang gets between them. Before further violence can ensue, Sykes calls his dogs back to his car, and they leave while making threats towards the gang and Oliver.
After this, a soaking wet Fagin returns to the barge, lamenting that he has only three days to find the money he owes Sykes. He discovers Oliver and, considering that they all need help, accepts him into the gang. That night, after reading a book, Oliver notices Dodger climbing into his bed to show that he loves him. Oliver runs toward him and brushes beside him. Dodger sees him asleep and smiles.
Next day, Fagin sets out into the city with his canine menagerie, Oliver included, and tries to sell his wares at a pawn shop, with no success. The animals, meanwhile, come face-to-face with a limousine driven by a butler named Winston. Winston is employed by the Foxworth family and is taking care of their daughter Jenny while the couple is out of the country. The dogs stage an elaborate ruse in order to get Winston out of the car. Tito and Oliver slip in and attempt to steal its radio to give to Fagin so that he'll have something to pawn to pay back Sykes. In doing so, Tito gets shocked by the electrical system which makes the car go haywire, and Jenny finds Oliver tangled up in the wires near it. Oliver finds a good home and a caring owner in Jenny, to the chagrin of Winston and the Foxworth's pampered, pedigreed poodle, Georgette.
The next day Fagin's dogs go to Jenny's house. After some initial disputes, Georgette is very happy that they are there to collect Oliver, and helps them take him back, convincing them that he's been traumatised by the whole experience and wants to go back to them. When Oliver is taken back, Fagin sees Oliver's new golden tag and the wealthy district he got it from, and sends Jenny a map and a letter requesting "lots and lots of money" as a ransom. Fagin then goes to convince Sykes that his plan is air-tight enough to pay him his money.
Jenny receives the letter and takes Georgette with her to go and get Oliver back, but Fagin's poorly drawn map leaves them both totally lost, although they do unknowingly arrive at their destination. Being distraught that his "wealthy cat-owner" is just a little girl with her piggy-bank, Fagin decides that he might as well return Oliver to her, and pretends to find him in a dumpster. However Sykes kidnaps Jenny, intending to hold her for ransom to her wealthy parents, and tells Fagin that their account is closed.
Fagin, who was not expecting Sykes to use him to perform an actual kidnapping, takes his dogs and Georgette to Sykes' shipyard to rescue Jenny, which the dogs, with Oliver's help manage to do. However an enraged Sykes and his Dobermans chase them down the city streets and into the subway in his car. Roscoe and DeSoto are both thrown onto the tracks in their fight with Dodger, and presumably killed. Jenny is thrown onto the hood of Sykes' car and Fagin tries to snatch her back while the dogs drive. They emerge onto the Manhattan Bridge, where Sykes' car collides with a train and he is killed, the remains of his car falling into the river. Tito manages to steer Fagin's vehicle onto one of the Manhattan Bridge's cables and they emerge unscathed.
The next morning, Fagin and the entire group celebrate Jenny's birthday party at her home. That same day, Winston receives a phone call from Jenny's parents in Rome saying that they will be back tomorrow, apparently earlier than expected. Fagin and his dog gang finally drive into the streets to make a new start.
