A pampered dog named Trouble must learn to live in the real world, while trying to escape from his former owner's greedy children.
Under the watchful eye of his devoted butler, James, and renowned animal trainer Cesar Millan, Trouble is a well-cared-for dog who lives the good life in a mansion with his wealthy and elderly owner, Mrs. Sarah Vanderwhoozie. One day, his owner passes away from natural causes, leaving him in her mansion alone and oblivious. Arriving to claim their inheritance are Mrs. Vanderwhoozie's niece and nephew, Claire and Norbert. As they are getting rid of her possessions and preparing to sell other valuables, they unintentionally and unconsciously get rid of Trouble, whom they immediately despise and ignore. However, in order for Claire and Norbert to legitimately inherit their aunt's wealth, they must first be able and willing to bond and take care of Trouble within three days. Only then can they sign the contract that their aunt's attorney, Mr. Macbain, has entrusted to them, much to their dismay. They employ Thurman Sanchez, a skilled animal tracker, to locate Trouble before the deadline after realizing he has gone missing.
After escaping the truck with his owner's possessions, Trouble discovers the truth about her passing and unintentionally destroys the nut storage in a red squirrels' tree. Trouble finds himself lost, alone, and resembles a stray after the squirrels take his collar as retaliation and flee. During a chase through a restaurant owned by renowned chef Ludo Lefebvre, Trouble encounters a stray dog named Rousey while attempting to get food from a meat truck in the city; Zoe Bell, a pizza delivery girl who aspires to be a singer, also loses one of her pizzas. After spending the night outside with Rousey following another run-in with the squirrels, Trouble goes into a dog park where he meets domestic dogs Norm, Gizmo, Bella, and Tippy. They help him find a home by letting him play in traffic, where he is picked up by Zoe and brought to her apartment. Zoe and Trouble start to get along, but only temporarily until she can figure out where he belongs and that she does not want her landlord to know. To prepare for a singing competition, Zoe composes a song and creates a new collar for Trouble.
Despite some unfavorable initial reactions, Trouble is confronted by Norm and the other dogs at the dog park the following day, and they voluntarily assist him after learning that the squirrels stole his old collar. Having finally located Trouble, Thurman inadvertently grabs the squirrel leader during the struggle and offers them a deal: a pile of nuts in return for helping him get Trouble. When Zoe briefly leaves Trouble at her apartment, the squirrels attempt to flush him out, creating a huge mess that leads to Zoe's landlord evicting her when she returns. Trouble is taken to the dog pound, where he makes friends with Snoop, Otis, and Caramel, three more strays, and reunites with Rousey. Trouble finds out from Rousey that she used to be an indoor dog just like him. Rousey's mistrust of people is explained by the fact that one day, after rescuing her owners' child from a car accident, they dumped her at the pound because they thought her bravery was aggressive.
Instead of competing in the singing competition, Zoe chooses to go to the pound and pick up Trouble on the day of the deadline. But she is already been outdone by Thurman. After riding off, Zoe searches the city for Trouble. Rousey chooses to assist the others in escaping and assist Zoe in finding Trouble after realizing how much she genuinely loves and cares for him. They track Trouble using his abandoned new collar, and they also enlist the assistance of the household dogs. After the twins fail to pay him as agreed, Thurman returns Trouble to Claire and Norbert at the mansion and, with the assistance of the squirrels, secretly promises retribution.
Claire and Norbert are about to claim their inheritance after lying to Mr. Macbain about their bond with Trouble when Zoe unexpectedly shows up and reveals the truth. Thurman comes in and tells Mr. Macbain more about the situation while demanding his money. Mr. Macbain rejects the twins' inheritance after discovering the truth. Thurman calls the squirrels to hold Trouble hostage because he still wants his money, but a fight breaks out when Snoop, Otis, and Caramel show up after following Rousey. Rousey shows up just in time to save Trouble's life as the squirrel leader holds him against a fan. Before the squirrels leave, she insisted on getting Trouble's old collar back. Following that, Mr. Macbain gives Trouble the authority to choose his owner. To the dismay of the twins, Trouble happily selects Zoe, and after signing the contract, she is able to inherit Trouble, the mansion, the assets, and his owner's fortune. Thurman departs with them. To her delight, Rousey is also adopted by James.
Renamed the Vanderwhoozie Dog Park and dedicated to both Mrs. Vanderwhoozie and Trouble, Zoe uses the funds to revitalize the dog park. She also starts pursuing her dream of becoming a singer, drawing the interest of well-known singer-songwriter Jason Mraz. To the delight of the dogs, Snoop, who was most likely adopted by Zoe, along with Otis and Caramel, then goes on to sing a song dedicated to Trouble.
