Ok so movie 2 starts out with a suspicious character, who is wearing a purple robe and a helmet made from a cardboard box, walking towards a decrepit abandoned building in the Ohkay City slums. He knocks on the door and the door opens a little to a bored-looking girl with a hoodie and pink hair who asks who he is and what he’s doing here. He answers that his name is Flippy and he’s come to join the group. The girl then sighs and yells out that there’s some dude named Flippy here to join the group and another voice (Petey’s) yells back to bring him over here. The girl then sighs again and brings Flippy inside and they walk down a hall where Flippy sees rooms filled with piles of loot and rooms filled with science and robot stuff.
He is particularly intrigued by a certain diamond ring and breaks away from the butler to look at it. Before he can get a closer look at it though, Petey comes up from behind him and asks what the heck he thinks he’s doing near his mom’s wedding ring. Flippy turns around and sees the butler, Petey, and Dr Scum all standing together. Flippy then takes off his disguise to reveal that he’s just a purple butterfly fish and the other three laugh at him until Flippy gets mad and lifts the butler into the air. After putting her down, the others are shocked and immediately agree to let him join their team and Dr Scum suggests that he outfit Flippy with some robot improvements to which the others all agree and they all start laughing maniacally.
Meanwhile, a ceremony is taking place at the city hall where New Mayor is holding a ceremony to reward Dog Man, Chief, and Sarah for saving the city. After giving Chief and Sarah medals of honor, New Mayor goes to Dog Man to give him one. However, Dog Man gets hyper and jumps on New Mayor doing to him what he usually does to Chief. Everyone is shocked and then Dog Man starts attacking the wreath of roses that says “congratulations” and he starts attacking people wearing hats. Chief tries to tell him to stop while Sarah apologizes over and over again to the mayor, saying Dog Man isn’t usually like this.
Eventually, Dog Man steals Mayor’s hat and runs away and Sarah chases him and catches up to him using her ex-spy agility. Sarah tells him to just hand over the hat and everything will be fine but Dog Man, who is still in a playful mood, instead smirks and runs away but he ends up bumping into a column and causing the building to start to collapse. Sarah and Chief look at each other in shock and Sarah tells Chief to get everyone out of the building while she uses her spy skills to hold the building together long enough for everyone to escape. After everyone escapes, Sarah tries to find Dog Man but she can’t find him and New Mayor lashes out at Chief and tells him to either fire Dog Man or be sent to Chief Jail. Chief pleads with New Mayor but New Mayor refuses to change his mind. Chief and Sarah look at each other with sadness in their eyes and then leave.
Meanwhile, Dog Man is at home, happily playing with New Mayor’s hat. Soon, his telephone starts ringing and Dog Man excitedly picks it up. He gets even happier when he hears Chief’s voice on the line but it quickly turns to sadness when Chief tells him he’s fired. He starts howling, hangs up the phone, and then starts playing sad songs and howling in tune with them. Meanwhile, Chief and Sarah are getting coffee together because Chief is sad about having to fire Dog Man and Sarah wanted to cheer him up.
They say loving words to each other and Sarah assures him that there was nothing he could do because it was either Chief goes to jail or Dog Man gets fired and the new chief would fire Dog Man either way. Chief feels better and he and Sarah hug. Meanwhile, Flippy’s robotic improvements have been completed and they all get milkshakes to celebrate and then they start laughing because now they can commence with their evil plans. A few days later, Dog Man is fat and has just been spending his time downing boxes of treats and watching tv shows like Supa Dog. He’s about to watch another episode of Supa Dog when Sarah’s news report interrupts the regularly scheduled programming and says that Ohkay City has been overtaken by a crime spree and Dog Man decides to stop being a lazy bum and help the city.
He makes a superhero costume similar to Supa Dog’s, grabs a few bones he bought from a crazy lady at a flea market, and then heads on out to stop the crime spree. He goes to the city center and starts fighting criminals who are being led by a certain superpowered fish cyborg. He eventually comes face to face with Flippy and they have an epic fight including Dog Man throwing a bone boomerang at Flippy, Flippy throwing him into a building, and throwing cupcakes at each other. Eventually, Flippy decides he’s had enough of this and just leaves. Sarah and Chief then arrive and congratulate Dog Man since there’s only one dog-headed person in Ohkay City.
However, at the same time, New Mayor also comes and he doesn’t like that Dog Man is getting attention so he sends Maude, his fav cop, to arrest Dog Man, which she does happily. Dog Man is loaded onto a prisoner transport vehicle and he looks at a horrified Chief and Sarah with fear in his eyes as he’s driven away.
Sarah and Chief then get in Sarah’s car so they can go to her apartment and form a plan to break out Dog Man from Dog Jail. Meanwhile Dog Man arrives at the jail which is on top of a dark and snowy mountain and comes face to face with a fat dude smoking a cigarette and smiling evilly. The dude then leads Dog Man into the prison where he sees all types of dogs with the same hopeless look on his face and the dude happily says no-one escapes the prison and then he shoves Dog Man into a scary-looking jail cell. He locks the door and walks away chuckling while Dog Man goes to the raggedy old bed to try and sleep but then he sees a dog skull and gets scared out of his mind and starts barking. Then, the dude comes back angrily and zaps Dog Man with a taser.
Meanwhile, Chief and Sarah have just arrived at Sarah’s apartment and Chief asks Sarah what’s the plan as she puts her things down and Sarah says to excuse her for a moment and she leaves. Chief sits down on a nearby chair and sees Zuzu who starts barking at him. Sarah then comes back wearing a black spy jumpsuit and says to come on and Chief, flustered by how pretty she looks, follows her as they go to a helicopter on top of the building. They fly to the jail and Sarah and Chief look for Dog Man before they see a sad little snout peeking out of the window wearing a mask and they fly to the window, break it, and then free Dog Man. The three of them then share a hug and Dog Man barks and says that they need to save the others and Chief and Sarah are confused but then they see him point to the jail.
Chief and Sarah agree but then they see on the news that Petey and Flippy are wrecking Ohkay City and Sarah scowls because it’s being presented by Sarah’s rival Timothy Helmeton. Chief tells Dog Man they can’t save the other dogs right now and Dog Man whimpers and Sarah says that she knows someone who can save them later and Dog Man starts howling happily and all three of them fly back to the city.
The three of them then arrive at the city where they see Petey sitting on top of a treasure chest looking vehicle shooting people with a gun that shoots out love arrows and the people that get shot are giving him their precious stuff. Meanwhile, Dr. Scum is standing on top of a robotic version of Philly the cheesesteak gyro that has laser eyes. Dog Man, Sarah, and Chief are about to spring into action when suddenly the helicopter shuts down. They all try to figure out what happened and they see that Flippy used his robotic enhancements to destroy all major systems on the helicopter and now the trio is freefalling as Flippy laughs maniacally and uses his laser eyes to destroy things (Dr. Scum rly likes the idea of laser eyes) and using his psychokinetic brain powers to bring him money and jewels from banks and jewelry shops. The trio is still freefalling when Chief realized he can do something and he grabbed a pen from his pocket.
Sarah asks if he’s going to write his last will and testament and Chief says no because he already wrote it and right now, everything’s going to the organization Ohkay City Donut Sellers. He presses a button on the side of the pen and a grappling hook deploys and lands on a gargoyle. They climb the rope and end up on top of a building as the helicopter crashes into the next building over. The trio then decides to make a plan on who’s fighting who and Chief says he’ll take Flippy and Dog Man points at Petey so Sarah says she’ll take Dr. Scum. They split up and Chief unhooks his grappling hook and this time hooks onto Flippy who gets mad and tries to shake him off.
Dog Man goes to Petey and barks at Petey, who just laughs and tells him to speak English because he didn’t take Dog Talk as his foreign language, he took French. This infuriates Dog Man and he jumps onto Petey and they engage in a fist fight and Petey asks his admirers to do something and one of them asks, “What do we do, oh fair Cupid captured in the form of a cat?” Petey says just do mob stuff so the admirers raid a shop called Bob’s Mob Supplies and chase the treasure chest vehicle thingy. Meanwhile, Sarah positions herself at a window in a high-rise facing Dr. Scum and Mecha-Philly and uses a tranquilizer gun to snipe Dr. Scum who then falls off Mecha-Philly and Sarah quickly grabs him before he falls to the ground because she wants him to face justice. She then gets on top of Mecha-Philly and tries to find a way to disable Mecha-Philly.
Flippy, meanwhile, is still trying to get rid of Chief and he decides to finally just look and shoot him with his laser eyes. Before he can though, he crashes into a building and passes out and Chief presses another button on his pen and deploys a parachute. Dog Man and Petey, meanwhile, are still fighting and Dog Man has the added challenge of the Petey admirers chasing him with pitchforks and torches. He then has an idea to grab the controller from Petey and he knocks down Petey, grabs the controller, and drives into a building causing the treasure chest vehicle thingy to be totaled. Dog Man, Chief, and Sarah, after finding Philly’s disintegration switch and pressing it, then find each other and hug each other.
New Mayor, with Maude by his side, then comes and angrily asks how Dog Man escaped and Sarah yells at him and says that Dog Man saved this city while New Mayor’s useless butt did nothing. New Mayor then apologizes and tells Maude to arrest the bad guy and he calls in some people who work at a mental hospital to find a way to rehabilitate the admirers. Chief, Dog Man, and Sarah then stare at the sky with resilient and determined looks on their faces. The scene then cuts to the police station where there’s a party to welcome back Dog Man and Dog Man is dancing in the center of the room and Chief and Sarah kiss while on the news (which no-one is looking at) it says that the Petey admirers have been successfully rehabilitated and Petey, Dr. Scum, and Flippy are all in jail. The scene then ends with everyone eating dog-friendly cake and Dog Man howling happily. Also, there’s a post-credit scene where Sarah’s twin brother and full time spy Hudson Hatoff bursts into Dog Jail with some fellow agents, frees the dogs, and takes the warden into custody.