Plot

Arnold and company must recover a stolen document needed in order to prevent the neighborhood from being bulldozed.

When a powerful developer named Mr. Scheck wants to knock down all the stores and houses in Arnold's neighborhood to build a huge "mall-plex", it looks likes the neighborhood is doomed to disappear. But with the help of a superhero and a mysterious deep-voiced stranger, Arnold and Gerald will need to recover a crucial document in order to save their beloved neighborhood.—Britney

When corrupt developer Schek threatens to buy the run-down urban neighborhood where a fourth grader Arnold lives, and now Arnold and his cool-as-ice best pal Gerald are on the biggest mission ever to save their neighborhood as they go up against a powerful industrialist who invades the city and buys everything in sight so he can knock it down and erect a huge "mall-plex." It's up to Arnold and Gerald to save their neighborhood before it's too late and they'll have to move somewhere else. But with the help of of a superhero and a mysterious deep-voiced stranger, Arnold and Gerald will need to recover a crucial document in order to save their beloved neighborhood at all costs.—Anthony Pereyra {hypersonic91@yahoo.com}

Arnold and Gerald must uncover an important document in order to save their neighborhood from a greedy developer. Sheck plans on destroying the neighborhood so that he can make a mega mall. With the future of their neighborhood at risk, Helga conspires against her father to help Arnold and Gerald. At the same time; Phil and the boarders, along with Big Bob (after realizing he will be swindled by Sheck) try to stop the construction crew from wrecking the neighborhood.—dawsonpersi

Arnold (Spencer Klein) and his pal, Gerald (Jamil Walker Smith), learn their beloved neighborhood is about to be torn down by a greedy developer named Scheck (Paul Sorvino) to build a mall. While the adults come up with a dodgy scheme, the friends try a more practical approach to the problem with the help of Helga (Francesca Marie Smith). The kids discover their neighborhood was designated as a historical landmark but they must prove it before Scheck moves in with his crew.—tpsimpleman

The film begins with several shots of Hillwood showing the kids having fun and adults doing their usual routine until Sid notices construction workers demolishing a house. Arnold and Gerald are then seen walking back to the boarding house with a popped basketball after being beaten by 5th graders at a game. Before Arnold walks into the boarding house, he sees several of his neighbors making a fuss about something. One of the gathered neighbors Mr. Green, explains the commotion. He states that Mr. Scheck, the CEO of a real estate company called Future Tech Industries or FTi, wants to buy all the houses in Arnold's neighborhood so the urban development firm can convert them into a futuristic mall.

According to the news, Mayor Dixie is already approving plans for the mall. This means that Arnold's neighborhood will be destroyed and everyone who lives there has to move away (which would also mean Helga would not see Arnold again or express her feelings to him). The neighbors state that they should do something about this. During the night, Helga discovers that her dad, Big Bob Pataki, is working with Nick Vermicelli (who had worked with Bob on previous occasions). Bob is revealed to be planning to build a store in Scheck's mall called "Big Bob's Super Beeper Emporium." Helga points out to her dad that people are going to suffer if he builds his store. However, Bob counters by saying that if they leave the neighborhood alone, his store will not exist. He also insists that change is good (as does Scheck at various times in the film) and states that when his store is built, their family will be rich and Helga will be able to buy anything. The next morning, FTi puts up a huge electronic billboard across the street from the boarding house that shows the number of days until construction begins as well as several Future tech Industries ads featuring Scheck stating "Out with the old, in with the new," "Change is good," and "I've seen the future, and the future is Future Tech Industries."

Arnold rallies the neighborhood and hosts "Blockapalooza," a block party held to protest against FTi. However, the permit allowing them to close a public street was stolen by Scheck's employees, and Blockapalooza was declared illegal. Arnold's grandmother was jailed for being hostile to the police suppressing the rally. She tries breaking out but keeps getting caught. As demolition day closes in, Gerald tells Arnold to stop looking on the bright side of things and that you cannot always win. Later, Arnold sees how this will effect the citizens as he sees the friendship between Sid and Stinky and the relationship between Mr. Green and his shop and how this will destroy his business.

Later on, as the boarders begin packing, Grandpa tells Arnold the history of the boarding house, stating that it was first built in the 1700's and it was the site of the "Tomato Incident" (a parody of the Boston Tea Party) during the Revolutionary War. The residents at that time angry over the increase in British taxes for tomatoes. The locals fought the British soldiers by hitting them with the tomatoes, sending them running. Arnold realizes that if he can find a document proving the event happened, then the neighborhood will be declared a historical site and cannot be demolished. With Gerald reluctantly tagging along, Arnold manages to trace the document to FTi, though Scheck denies ownership of the document. Just as Arnold and Gerald are about to give up hope, the boarding house telephone rings, and a mysterious individual named "Deep Voice" reveals that Scheck is lying and the document is hidden in his vault, which Vermicelli has the key to. Gerald suggests going to a woman named Bridget who can provide them with the proper gadgets to do the job and sneak the key away from Vermicelli. Arnold and Gerald, now secret agents, follow Vermicelli to a bar, where they disguise themselves as employees. Arnold and Gerald use one of the gadgets to listen to what Vermicelli is saying. Vermicelli's voice is heard over the speakers, and people are confused and wonder about the key that Vermicelli had mentioned. Vermicelli gets angry and accidentally spills his drink. He demands that Arnold and Gerald clean up his mess and replace his drink. Arnold's fake mustache almost slips off, nearly revealing him to be a kid. They walk away, and before Vermicelli can figure out who they are, they leave the bar. Arnold and Gerald follow Vermicelli to his home outside of Hillwood and stay on top of his roof until he eventually falls asleep. Arnold straps himself to a rope to swing down and sneak the key. Gerald is holding on to it, but let's go when his watch beeps. Arnold almost falls down, but Gerald grabs it just in time. Vermicelli wakes up when Arnold's sweat touches his forehead, but luckily, he thinks that Arnold is an angel and goes back to sleep. Arnold gets the key and they leave the rooftop. Deep Voice gives them a call and gives them more information on what they need to do. The bus picks them up and they head to FTI. Big Bob, having read the fine print of his contract, finds that Scheck had taken control of 51% percent of his company in exchange for the right to build his beeper emporium, and takes his anger out on Vermicelli. They engage in a small fight before Bob is dosed in pickle juice (reminiscent of the Hulk) and knocked out. Vermicelli then realizes that the key was gone and alerts Scheck.

Meanwhile, Grandpa Phil and the men at the boarding house are trying to develop a backup plan just in case Arnold fails to get the document. They have several ideas, but fight on their weaknesses. However, Phil gets an idea that works. They plan to wire the sewer tunnels beneath their street with dynamite. They would then ignite it and blow a huge hole in the ground so the Future Tech workers would fall in. Arnold and Gerald infiltrate the FTi building and locate several different vaults. When they finally unlock the right vault, they find the document missing. Scheck comes up from behind them, with the document in his hand. He reveals that his ancestor, who was the German leader of the British forces, was humiliated by the Tomato Incident. For generations, Scheck's family has been planning on regaining control of the city and get revenge against the boarders.

Scheck then burns the document in front of them. His bodyguards then arrive to detain Arnold and Gerald, who manage to escape and split up. When Arnold is just about to give up hope, he receives another call from Deep Voice, and remembers that FTi has cameras everywhere. He manages to get a video of Scheck burning the document. However, security forces arrive, forcing Arnold to hide on the roof. Meanwhile, Gerald searches for a cab to take them back to the neighborhood. Arnold is then contacted by Deep Voice once again, who is then revealed to be Helga, who, after some pressing from Arnold, confesses her romantic feelings for him and kisses him at the top of the tower. They escape the building and meet Gerald on a city bus. But the driver Murray is unwilling to speed up until he realizes that his former flame lives near Arnold and that her house is going to be demolished. They then ensue into a high speed chase to get back to the neighborhood before Scheck, who is chasing after them in his car and trying to kill our heroes in anyway possible to prevent them from stopping his plans. Scheck tells his workers to let up the bridge so the bus can't cross, but they make the leap, and Murray becomes unconscious. Murray's foot is stuck on the gas pedal. Arnold tells Gerald that he must drive. Though reluctant at first, Gerald eventually is convinced that he must drive it, while Arnold and Helga control the other gears. They almost run over man walking across the street. Phil and the others are waiting with their explosives for FTi to begin taking the neighborhood down. The FTI workers are going to destroy the neighborhood with people still there and inside the buildings. Big Bob is in the area and discovers Phil's plan. Although Bob states they could do some serious jail time, he decides to help because Vermicelli double-crossed him.

Meanwhile, Vermicelli's workers blow up the overpass to prevent Arnold, Gerald, Helga, and Murray (who is unconscious at the time) from getting to the neighborhood. However, a truck on the freeway that had a ramp on the back was stopped near the edge. The quartet ride the bus over the truck's ramp to jump the hole and make it to 33rd Street. Back at the neighborhood again, Grandma (who has escaped from jail) hijacks one of the bulldozers and destroys the rest. Soon, a rogue bulldozer and the city bus that Arnold, Gerald, and Helga are on collide. The three kids come out okay a few moments later. Mayor Dixie arrives and Bridget gives Arnold a VCR to show the tape of Scheck burning the document. Bridget hooks it up to the big Scheckivision screen and Arnold shows Mayor Dixie the tape, who then proceeds to claim the neighborhood as a historical landmark. The citizens of the neighborhood cheer for Arnold and Gerald for their bravery and for saving the neighborhood.

Scheck then arrives but is dismayed by the incriminating evidence. He gets into his car and tries to run over Arnold and Gerald, only to find that Grandma stripped his car of its wheels. He is then arrested for his crimes and Big Bob gets in another fight with Vermicelli, knocking him out. Arnold's neighbor Harold is exhausted because the exploding freeway woke him up. He sits down on the button that ignites Phil's explosives. The explosives beneath the streets ignite, destroying the FTi billboard. Phil and the boarders run away from the police, and Murray reunites with his ex-girlfriend Mona. As Arnold and Helga watch them, they begin talking about the events of that night and agree that it was all "in the heat of the moment." (As neither of the two were ready to deal with the fallout of the confession.) Arnold and Gerald do their handshake and talk about how they saved the neighborhood. Arnold reminds Gerald that their ball is flat, but Gerald tells him that it's just a little low on air. Arnold questions Gerald's positivity, and Gerald tells him that somebody had to do it, just like Arnold said to him at the beginning of the film. The movie ends with Helga running cheerfully as Eugene sings a song about the neighborhood being saved, but Gerald interrupts the song and tells him that the show is over.