Trouble is a pampered dog who enjoys a luxurious life in a mansion owned by his elderly caretaker, Mrs. Sarah Vanderwhoozie. Under the watchful care of his devoted butler, James, and with the help of renowned animal trainer Cesar Millan, Trouble has everything he could wish for. However, everything takes a turn when Mrs. Vanderwhoozie passes away unexpectedly. This leaves Trouble alone in the mansion, unaware of the impending changes that await him.
Her niece and nephew, Claire and Norbert, come to claim their inheritance, but their disdain for Trouble is evident from the moment they arrive. As they begin rummaging through Mrs. Vanderwhoozie's belongings to prepare for the sale of the house, they completely overlook Trouble, neglecting him in the process. In a surprising turn of events, they soon discover that they cannot inherit their aunt’s wealth unless they manage to bond with and take care of Trouble for three days. If they fail, all is lost. Perplexed by their situation, they hire an animal tracker, Thurman Sanchez, to locate Trouble after he mysteriously goes missing.
As Trouble escapes from the moving truck with his owner's belongings, he stumbles upon the reality of his owner's passing. In a moment of chaos, he inadvertently destroys the nut storage of a tree filled with red squirrels, leading to a series of unfortunate events. Now lost and alone, without his collar, Trouble resembles more of a stray dog as the squirrels take their revenge and flee.
During a frantic chase for food in a bustling city, Trouble meets a stray dog named Rousey when they both try to enjoy food from a meat truck, resulting in a hilarious encounter with renowned chef Ludo Lefebvre. As night falls, Trouble finds temporary solace by sleeping outside with Rousey. They soon explore a nearby dog park, where they encounter other pets, including Norm, Gizmo, Bella, and Tippy, who offer to help him find his way home.
Despite the initial troubles he faces, Trouble's luck seems to turn when he meets Zoe Bell, a pizza delivery girl with dreams of becoming a singer. She takes him to her apartment, and although they develop a close bond, Zoe knows that she has to find Trouble’s rightful home. Driven by her aspirations, she writes a song and creates a new collar for him.
The next day, Trouble confronts Norm and the other dogs in the park, who generously assist him after hearing about the squirrels taking his collar. Meanwhile, Thurman's search leads to unexpected antics, and when he tries to catch Trouble, he mistakenly gets hold of the squirrel leader. A desperate negotiation ensues: a mound of nuts for Trouble’s freedom. However, when Zoe briefly leaves Trouble alone, the squirrels wreak havoc, resulting in her landlord evicting her upon her return.
At the dog pound where Trouble finds himself next, he reunites with friends Snoop, Otis, and Caramel. Together, they discover Rousey, who reveals that she once had a home of her own but was abandoned due to her courageous reputation during a family's crisis. Feeling empathy for her plight, Zoe decides to save Trouble instead of competing in her singing contest on the day of the deadline, but soon realizes that Thurman has beaten her to it.
When it seems like all hope is lost, Rousey makes a brave decision to help Zoe rescue Trouble, leading them on a daring chase through the city. They utilize Trouble's old collar to track him down, enlisting the support of other nearby dogs. However, after a troublesome encounter and failure to receive their payment from Thurman, he returns Trouble to Claire and Norbert, who are on the brink of claiming their inheritance.
Just as they lie to Mr. Macbain about having bonded with Trouble, Zoe arrives and reveals the truth. Thurman attempts to leverage his status, but the tables turn when Mr. Macbain uncovers the deception. A showdown erupts as Snoop, Otis, and Caramel rush in to support Trouble. In a dramatic moment, Rousey arrives just in time to save Trouble from a dire situation, securing his old collar back from the mischievous squirrels.
Ultimately, Mr. Macbain grants Trouble the choice of his new owner. In a twist of fate, Trouble chooses Zoe, much to Claire and Norbert's dismay. With her victory sealed, Zoe inherits not just Trouble, but the mansion and a portion of Mrs. Vanderwhoozie’s fortune. The bond solidifies as Rousey is also adopted by James.
With newfound resources, Zoe revitalizes the dog park, renaming it in honor of both the late Mrs. Vanderwhoozie and Trouble. She tirelessly pursues her musical dreams, attracting the attention of the esteemed singer-songwriter, Jason Mraz, while the story concludes with a joyful celebration as Snoop, Otis, and Caramel perform a song dedicated to Trouble.
