Plot: After a tragic bomb incident leads police officers Matthew Knight and Greg the Dog severely injured, their only hopes of survival is to become one being: Dog Man. As Dog Man struggles to cope with his new identity, the world's most evilest cat, Petey, attempts to destroy him. In Petey's latest plot, he creates his own partner in crime named Li'l Petey. However, Li'l Petey becomes the solution to Dog Man's loneliness, which Petey does not really like...
The film itself: After the opening logos, the screen fades to see a young Matthew Knight at a dog shelter. He looks through all the dogs, as we see dogs from throughout the series, like Zuzu, Mr. Stinkles, and many dogs that were incarcerated in Dog Jail in Brawl of the Wild. However, Knight then comes across the perfect puppy: Greg. We then cut to the opening credits, as we see time go by as Knight and Greg train to get into the cops. Eventually, as the opening credits end, Knight and Greg are seen getting ready for their interview with Chief. The two get in Knight's car and leave. As they head to the cops station, we see the entirety of Ohkay City, including a wanted poster of Petey the Cat.
Eventually, they get into the cops station and see all the cops working. Maude sees the two and stares at them suspiciously, unnvering Knight. They end up going to Chief's office and have their interview, easily passing. Chief tells them to come to the station the next day at seven, and the newly hired cops run out of the station, grinning ear to ear. They tell Knight's girlfriend Alice how they got hired as she congratulates them. Knight and Greg then head to bed.
The next day, Knight wakes up with his phone buzzing like crazy. Knight checks his phone and sees 50 missed calls from Chief. He then checks the time. 9:00. He screams and quickly changes into his cop attire and gets into the car with Greg. They go as fast as they can to get into the station, where they come across the angriest police chief ever seen in the universe. He then yells so loud at the two that it was heard by none other than Petey in his secret lab.
Petey looks out and sees that Knight and Greg had been kicked out of the station. Petey becomes aggravated that Chief had hired Knight and Greg and wanted to stop the two before they arrest him. So he gets a bomb and sets it outside. Hearing the ticking, Knight and Greg run to see the bomb. Knight asks Greg which wire they should cut, to which Greg responds with a growl. Knight takes it as "green" and cuts the green wire, resulting in the bomb exploding. Knight and Greg are rushed to the hospital, where the classic Dog Man surgery happens.
After Dog Man is created, Chief sends Dog Man back to the police station. When they arrive, all of the cops simply stared at Dog Man, who was walking on all fours. Chief then tells Dog Man he had to stand on his hind legs, which Dog Man does so, but stumbles while doing so. Everyone cringes, while Maude giggles a little. Chief then walks away in both embarrassment and disgust, making Dog Man feel down as he walks to Knight's desk, which had the name Knight crossed out and replaced with "Dog Mna". Dog Man simply sighs as he sits down and places his head down on the desk. Maude, who was the desk next to him, simply laughs at Dog Man.
Meanwhile, Petey reads a newspaper about the creation of Dog Man in disgust, having failed at destroying Knight and Greg and decided he had to destroy Dog Man at all costs. Petey creates numerous ideas on how to destroy Dog Man, creating the vacuum cleaner robot, Robo-Chief, and the Robo-Brontosaurus. He laughs evilly as he starts creating the robots.
Meanwhile, Dog Man leaves the police station and goes home for the night. That's when he goes into Knight's house, only to find out that Alice had moved away. Dog Man becomes absolutely depressed: his family is either gone or dead, and society just thinks he's a weirdo. He goes back to the police station and sleeps behind a plant inside the cops. Dog Man then wakes up to Maude and the Mean Cop laughing at him. Dog Man growls at the two, scaring the Mean Cop. However, Maude just smirks and growls at Dog Man. He hides behind the plant again, leading to Maude laughing again. Maude then mocks him and tells him he doesn't belong as one of the cops, nor to society. She then laughs mockingly alongside the Mean Cop. Dog Man lies down in shame.
Meanwhile, Petey had just finished building his deathly robots and turned them on, saying a montage would be needed to show how excellent these robots would be in destroying Dog Man. He evens says that it will be done in Flip-o-Rama, as Flip-o-Rama pages start showing, with Petey narrating and making it look like Petey was winning. However, after the montage, we cut to Petey in a prison uniform behind bars, with him saying that none of it actually happened, and Dog Man eventually got him. The screen then pans to the city celebrating Dog Man, as the camera pans to Dog Man, who starts to stiffle a smile. He then looks out at Chief. Chief gives him a small smile, indicating that Chief was proud of Dog Man.
That evening, Dog Man is sent a text message from the mayor, giving him instructions to a brand new doghouse just for Dog Man. Dog Man howls with joy at the sight of the house and comes in, noticing that the house was much bigger on the inside. He takes out everything that was his: a family portrait of Knight, Greg, and Alice, and his tennis ball. He then looks around the whole house. His own house, all by himself. However, he realized that it looked a lot like Knight's house. Then came the realization that he would basically live in his old house all by himself. All dogs hate living by themselves for a long time, but to Dog Man, it seemed like forever. He lied down on the bed that was in the house and just slept, pretending to be happy when it was obvious he really wasn't.
Meanwhile, in Cat Jail, Petey is shown devising a plot to escape the prison with many other cats from Cat Jail. The plot involved them all, and after creating it, they immediately went into action. During lunch, Big Jim would distract one of the guards by showing him how much food he could fit in his mouth. Meanwhile, Mr. Whiskers would knock out the other two guards. Tippy would grab one of the keys from the guards and unlock the door, and Fluffy would be able to make sure there were no alarms. Everyone outside of Big Jim was able to get out of prison, and they would each help each other get past the prison walls. Fluffy was the first person to get out because he was the lightest of them all. After that, Petey was lifted out. However, unlike the plan, Petey threw Fluffy back inside the prison, knocking down everyone, and ran away free, as the guard who Big Jim distracted found out about the escape and took everyone else back inside.
The news of Petey's escape from jail traveled throughout all of Ohkay City, including the mayor. The mayor was furious at Chief and Dog Man for doing nothing about Petey's escape and threatened to fire Chief, replacing him with Maude. After she left, Chief became extremely saddened, and Dog Man realized Chief was only harsh on Dog Man because the mayor was harsh on Chief. So, Dog Man cheered him up, which made Chief realize he was way too harsh on Dog Man for everything. The two hug each other after their realizations.
Meanwhile, in Petey's lab, Petey realized that if Dog Man was able to arrest him so easily, he would need an assistant to back him up and help him destroy Dog Man. Therefore, he orders and collects a cloning machine and uses it to create Li'l Petey. After Petey declares that Li'l Petey is not his son, Li'l Petey cries for hours, making Petey instantly regret ever creating Li'l Petey.
Meanwhile, Chief starts giving Dog Man multiple gadgets and weaponry to help find Petey, such as a gun and binoculars. Dog Man takes them with him to his house, where he goes by his family portrait. Dog Man starts to reminisce about all of his and Knight's happy moments together, such as meeting Alice or when he cheered Knight up when he was down and nearly thought he couldn't get into the cops. Now, there won't be any more of those memories. He walked back to his bed gloomily.
Meanwhile, after a long night hearing nothing but Li'l Petey's crying, Petey could do nothing except give Li'l Petey to someone else. So, he went out and tried to see if anyone wanted him. Dippy comes and asks how much Li'l Petey cost, even though Petey made it clear that he was completely free. After Dippy left, without Li'l Petey, the latter had to use the bathroom, giving Petey the chance to leave him. When Li'l Petey comes back, he sees no one.
Meanwhile, on a helicopter, Dog Man was using binoculars to figure out where in Ohkay City Petey was. However, instead of seeing Petey, he found Li'l Petey, alone, in the dark. Dog Man has Chief park closer to Li'l Petey, where Dog Man would take in Li'l Petey. After they go to Dog Man's house, Li'l Petey asks Dog Man to read him a bedtime story. Dog Man reads him the Squirrel book, allowing Li'l Petey to fall asleep.
The next day, Li'l Petey wakes Dog Man up and shows him a homemade book talking about how much Li'l Petey loved Dog Man for taking him in. Reading this made Dog Man realize that Li'l Petey was also lonely, and taking him in was the best choice. The two then spend the next few days having fun with each other, similar to the scene that was in the original film. Afterward, the news of Dog Man with Li'l Petey got to Petey. Upon hearing the news, Petey realized that he could just destroy a loved one of Dog Man to break Dog Man. So, he creates 80-HD and has him find where Li'l Petey went. 80-HD then quickly leads Petey to Dog Man's house, and they grab Li'l Petey.
The next day, Dog Man wakes up to find that Li'l Petey was gone. This instantly terrified Dog Man, as Li'l Petey was his only friend left. Dog Man then realizes one thing: he must've been kidnapped. And who else could've kidnapped him than his arch-nemesis? Dog Man starts sprinting away to Petey's lab. There, he finds that Li'l Petey had been tied up behind a chair. Petey just evilly grins. Dog Man pulls out his gun, threatening to shoot Petey. Petey just puts his arms up in the air. But then, he moves his tail to grab the gun, and points it straight at Li'l Petey. Petey smirks at Dog Man as he starts to pull the trigger. Dog Man then angrily kicks the gun out of Petey's hands. Petey takes it as a start to a fight, and punches Dog Man. A fight ensues between the two, until Petey accidentally scratches at the chair holding Li'l Petey, freeing Li'l Petey. Li'l Petey gets out of the chair and yells the two of them to stop. Li'l Petey then asks why Petey was doing all this. Petey explains that when he was young, his father abandoned him and his mother and not too long later his mother got ill and died. Li'l Petey then hugs Petey, filling Petey with remorse for all his actions. After the hug, he puts down Li'l Petey and puts his arms out, telling Dog Man to arrest him. Dog Man smiles at Petey's remorsefulness and handcuffs him.
The next day, Dog Man takes Li'l Petey with him to the police station, where Chief made the honors of creating a party to celebrate the successful arrest of Petey. Everyone cheers for Dog Man and celebrates him, showing that they had all gotten rid of their old thoughts about the cop. Except, of course, for Maude, who isn't seen anywhere in the station. As everyone cheers for Dog Man, the screen fades to black as the end credits start.