Plot
Dog superstar Rexxx lives the high life-with adoring crowds, a loving owner and an array of best-selling blockbusters under his belt. However, when his owner, Trey tries to convince him to perform a skydiving stunt, the plane malfunctions caused by a lightning strike and Rexxx is sent tumbling from the sky, landing in a tomato truck. While Trey mourns his apparent death and begins regretting his failure in not treating him like a 'real dog', Rexxx settles into an abandoned warehouse, desperately missing his owner.
Meanwhile in the city of South Harbor in Lincoln County, Shane Fahey is struggling with the death of his uncle, Capt. Marc Fahey, and Blue (The former "Firehouse Dog") after being trapped in a fire in a disused textile mill. Realizing he forgot to study for a test, Shane ditches school, but is quickly caught by two other firefighters, Lionel and new recruit Terrence. Arriving back at the fire station (known as 'Dogpatch' home to Engine 55 & Rescue 26) in disgrace, he is chastised by both driver Joe and his father Connor, the recently promoted Captain of the station, who is having problems of his own; the station is about to be closed due to a lack of funding and overall bad publicity. However, before Connor can properly address his son's problems, Dogpatch is called out a fire in a derelict apartment building. Due to a slow suit up and Engine 55 having engine trouble, the team is the last to arrive and is put on standby by rival Greenpoint stations Captain Jessie Presley. Shane notices a terrified Rexxx balancing on top of the burning building; Connor manages to rescue him, and orders Shane to put up 'Lost Dog' flyers. Due to the name on his collar, which is a prop from the filming at the time of Rexxx's accident, the station renames the dog 'Dewey', and keeps him at the station until someone comes to claim him.
Whilst city manager Zachary Hayden reminds Connor of the station's upcoming shutdown, Shane struggles to cope with Dewey's spoilt needs and strange habits. Realizing that the dog is fast and active, Shane enters him in a firefighter's competition, where they are pitted against rival fire station Engine 24 Greenpoint. Although Dewey initially beats the other station's score, he is distracted by their Dalmatian, who reminds him of a female Dalmatian that broke his heart. Despite losing the competition, Shane and Dewey begin to bond.
The next morning, the station is called out to a tunnel collapse. Everyone has already been evacuated upon their arrival, but Capt. Fahey spots that a Captain Presley is unaccounted for and initiates a search. Connor rushes into the wreckage, and Shane, fearing for his father's safety, allows Dewey to run in after him. Dewey manages to alert Connor to Jessie's presence, subsequently saving her life. Following this, the station begins to gain popularity, as they realize that Dewey could become a potential firehouse dog. Due to this change in circumstances, Zachary notifies them that the station is saved.
However, Shane's excitement is lost when he discovers his father has moved to his uncle's former office. Angered that his dad is trying to take his uncle's place, he roots through the files, where he discovers an unnerving number of suspected arsons, within the general area of the station. Upset that Shane felt he was being neglected, Connor makes an effort to reconcile with his son, and is shocked when Shane reveals that he feels guilty for being relieved that it was his uncle who died instead of his father. Later on that night, Dewey is awarded a medal for his bravery at a firefighter's gala. However, he ends up reuniting with Trey upon spotting him among the attendees; Connor reluctantly allows an ecstatic Trey to keep the dog.
A few hours later, however, Dewey escapes Trey's hotel room to chase after the station's engine, which was called out to another fire on a garbage barge at the City Harbor. The team is only too happy to allow him to climb on board. At the fire they struggle to put it out; meanwhile, Shane returns to the station to discover that the fire was simply a decoy, so that the suspected arsonist could burn the "Dogpatch" station to the ground. Panicking, he calls his friend, Jasmine 'JJ' Presley to work out what to do, before hearing footsteps upstairs, which turn out to be the arsonist.
Ignoring JJ's warnings, he heads upstairs to confront the arsonist. To his horror, he realizes that the arsonist is in fact city manager Zach Hayden, who wanted to burn buildings in Engine 55's patch in order to build a football stadium for City Chief Corbin Sellars – killing Shane's uncle in the process. After the station's closure was denied, he had no choice but to burn it down himself, but didn't realize that Shane was still in the building. The two become trapped inside the burning building when Zach's incendiary device ignites. Shane loses consciousness and Zach is forced to leave the building.
Meanwhile, Dewey – sensing that Shane is in danger – races back to the station as Connor follows behind, having been alerted to the fire by Jessie. Dewey finds Zach trying to escape, and traps him in a phone booth (which he also escapes from) before finding Shane. Dewey revives him by licking him and then Shane and Dewey try to find a way out of the burning fire station. Connor arrives on the scene, only to find the station completely inaccessible. Hearing Dewey's barking, he eventually manages to break down the garage door and finds a terrified Shane. Shane manages to convince him to pass him his axe through some broken glass so he can try to break the hinges himself; Dewey then leads them out. Shane manages to tell Connor about Zach’s arson attacks before he is put on oxygen. Furious, Connor confronts Zach and Pep gets her own payback on him before the other Dogpatch firefighters hand him over to the police.
Corbin Sellars' scam is exposed and he is also arrested. Following the events of the fire, all of the firefighters of the station are awarded medals, including Shane and Dewey. Upon seeing how happy Dewey is with them, Trey allows Shane to keep him, adding that now that Dewey has been a true hero, he won't be content with just acting like one. Both Shane and Connor are overjoyed, with Dewey realizing his true potential as a firehouse dog. "Dogpatch" is repaired and restored from the fire damage it sustained, and Engine 55 receives a brand-new 900bhp engine. The team head off to a grass fire with Dewey following behind.
