In Miami, Florida, although he often forgets how to drive, Dibley (Gabe Kaplan), a man with "recurring amnesia," drives his friends, Charlie Swaboda (Alex Karras) and Walter (Robert Klein), to their psychiatric appointments. Swaboda has a "parental fixation" and brings his mother with them, unaware that "Mrs. Swaboda," is invisible to everyone else. Mild-mannered Walter is a schizophrenic with two additional personalities: "Rocky" is a belligerent gangster, and "Kitty" is modeled after actress Bette Davis. As they drive home from the appointment, road construction detours them to an unfamiliar part of town. Dibley runs over an enormous pothole and his car breaks in half. He declares that the city is responsible for damages, since the pothole destroyed his car. Dibley, Swaboda and Walter go to City Hall, looking to get reimbursed $650 for the cost of the car. However, a clerk declares the city is not liable for damages because the men did not file a complaint about the pothole prior to the accident.At home, Dibley tells his girl friend, Carol (Susan Clark), about the incident, but they realize he has no recourse. Later, as they watch a war movie, the film's naval bombardment inspires Dibley. The next morning, he tells Walter and Swaboda that they will take the money the city owes them. The mayor (Arthur Rosenberg) plans to host a luncheon at his home, and Dibley wants to threaten the mayor with a naval bombardment. Carol reluctantly agrees to help, on the proviso that she can call it off if the situation looks too dangerous.Their first step is to get a cannon from the local armory. Only soldiers are allowed inside, so they go to a costume store to obtain National Guard uniforms. Dibley cannot be the point person because he constantly forgets what he is doing, and Swaboda will only go if he can bring his mother, so Walter is chosen. When he walks into the armory, the "Rocky" personality takes over, and claims to be General MacArthur. The flustered assistant ushers Walter into an office, then gets his colonel. However, when Colonel Brogan (Al Kiggins) meets Walter, the "Kitty" personality has taken over, and the plan fails.Later, Dibley and Carol see a flatbed truck hauling a tank. They follow the vehicle to the docks, where several cannons are behind locked gates. When the dock workers break for lunch, Dibley approaches Randall Kendall (Peter Bonerz), the crane operator. Dibley claims to be a top secret government agent and convinces Kendall that the shipping company is committing treason by secretly sending arms to the Soviet Union. Dibley insists he needs a cannon for proof and Kendall offers to help.Next, Carol, Dibley, Walter and Swaboda go to a used car lot to get a vehicle to transport the cannon. Dibley plans to take a Jeep for a long test drive and return it after their mission is complete. They get into a Jeep and drive toward the exit. However, a police car is parked outside, so Dibley re-parks the Jeep on the car lot. A salesman walks over, assumes they just drove in to sell their car, and offers $1,500 in cash. They accept the money and the salesman walks away. Another salesman comes over and offers to sell them the Jeep for $1,500. They give him the cash and drive away. Dibley coordinates with Kendall, who worries about the other dockworkers, so Dibley devises a plan to distract them.The next day, Dibley rents a boat, speeds to the waterfront, and plays loud music to attract attention. He announces that Carol is a stripper and the dockworkers rush to see her undress. Meanwhile, Swaboda and Walter drive the Jeep to the front gates and Kendall's crane lowers the cannon over the fence. As Walter and Swaboda drive away, Carol falls overboard and the dockworkers turn back to work. Back at Dibley's home, Carol is frustrated and wet. She heads inside while the guys go to lunch.At a restaurant, "The Boss" (Alex Rocco) and two of his thugs, Knuckles (John DiSanti) and New Yorker (Bobby Ramsen), discuss their plan to rob an armored car and realize they need a diversion for the police. Dibley, Walter, and Swaboda sit at the table behind the robbers and discuss their plan to load the cannon onto the inter-island ferry, cruise to the mayor's mansion, threaten a naval bombardment, and get their money.As they leave, Dibley realizes that he forgot his shoes. As he crawls under the table to retrieve them, Dibley overhears the Boss say the cops will rush to the mayor's luncheon to stop the "bombardment," and it will be the perfect diversion for the armored car theft. When Dibley tells the others, Carol wants to go to the police. However, Dibley is determined to execute his plan and stop the armored car theft. Dibley insists they have everything under control, including Coast Guard uniforms for the men, and a nun's habit for Carol.Dibley, Walter and Swaboda drive the cannon to the waterfront, commandeer the ferry, and tell the captain that it is quarantined because of possible yellow fever contamination. Dibley insists the mayor wants to personally view the ferry and orders the captain to speed to the mayor's mansion. When the ferry anchors outside the mansion, Dibley aims the cannon and telephones the mayor. The mayor offers half a million dollars, but Dibley only wants the $650 plus expenses, and explains the pothole situation. Sensing a political opportunity, the mayor offers to pay out of his own pocket if Dibley does not tell anyone about the bombardment and lets everyone believe the mayor heard of the situation and stepped forward to solve it. Dibley agrees and tells the mayor to put the money in a bag and hand it to a roller-skating nun at the docks. He informs the ferry boat captain that the mayor determined the ferry is not contaminated and they return to the docks.When the mayor arrives with the money, Carol waves at Dibley, Walter and Swaboda as they speed away. Carol informs the mayor about the armored car heist, and he insists on helping. The Boss and his men detour the armored car to a construction site, and drop a wrecking ball on the vehicle to open it. The Jeep races toward them, so the Boss and his men get in the armored car and drive off. A chase ensues involving the Jeep, the mayor's car, and an additional police vehicle. Dibley eventually pulls in front of the armored car, planning to stop it with the cannon. However, he suddenly forgets how to drive and stops. Walter's "Rocky" personality emerges, grabs a shell, loads the cannon and fires. It misses the truck, but creates a huge pothole that the truck crashes into. Police capture the robbers, and the mayor thanks Dibley and his friends for their help.Later, the four friends are driving in their new car. They approach a huge pothole and the others react, but Dibley smoothly avoids it. He pulls to a stop in front of the hole and claims he is cured. However, instead of driving forward, Dibley reverses into the pothole. As they get out and look at the destroyed car, Dibley insists that this time they will not bother with City Hall, he has a better idea. Dressed in naval uniforms, they plan to commandeer a ship.