The year is 1935 (where a car smashes down the title caption in the first of several sight gags throughout the movie). A pet shop owner catches a young boy shoplifting a puppy. To discourage the kid from a life of crime, the owner tells a story....The year is 1910. Young Johnny Kelly (Byron Thames) is a poor but honest newsboy in New York City. Johnny beats up Danny Vermin (Georg Olden) in self defense and discovers his mom needs an operation they cannot afford. Since the execution of Johnny's father, Killer Kelly, his widow, Ma Kelly (Maureen Stapleton), has supported Johnny and his younger brother, Tommy, who is fascinated by the law.Johnny's fight with Vermin attracted the notice of local crime boss Jocko Dundee (Peter Boyle), and Johnny, seeing no honest way to earn the money for his mom's operation, sees no choice than to do a job for Dundee, even though it probably means breaking the law, and in doing so, "breaking his mother's heart". He helps Dundee rob the nightclub belonging to Dundee's rival, Roman Moronie (Richard Dimitri). When asked his name, Johnny coins the name, "Johnny Dangerously", but Moronie, a malapropist of swearwords, never "forgets a fargin face."Several years pass by. With his mom's continuing medical problems, the adult Johnny (Michael Keaton) goes to work for the Dundee gang full time. He becomes a suave young man, with plenty of folding cash. The whole neighborhood, including the local Pope (Dom DeLuise) knows that Kelly is really Johnny Dangerously, but Johnny's secret identity is carefully concealed from his brother and mother. They think he is a law-abiding nightclub owner. Similarly, the gang knows nothing of Johnny's mother and brother. Tommy (Griffin Dunne as an adult) is now in law school, with a girlfriend, and somewhat of a prighe wants to drop out of law school so he can get a job, marry his girlfriend, and "get laid." With the assistance of a public health film ("Your Testicles and YOU"), Johnny gets him to go back to law school.Johnny comes to Dundee's headquartershe is still involved in a running feud with Moronie find he has taken on two new gang members: Danny Vermin (Joe Piscopo as an adult), and his sidekick Dutch. Danny has lived up to his potential and become a total scumbag, with a taste for using opera audiences as shooting galleries with his .88 Magnum pistol. Moronie, subtle as always, sends a robot with a machine gun to try to knock off the gang. He is not successful, and Johnny retaliates by knocking down Moronie's club (which was in need of expansion anyway) with a bomb dropped from a biplane.The two gangs go to war. In the meantime, Johnny falls for a young showgirl new to the big city, Lil Sheridan (Marilu Henner), who, when she meets Johnny for the first time, asks him, "Do you know your last name is an adverb?". They go for a long walk together, ending in sexual fireworks.The gang war continues. Moronie sends a plumber to plant explosives in Dundee's toilet. Dundee has a narrow escape, and he retires in Johnny's favor. Johnny negotiates a truce with Moronie.(Note: another running gag has Ray Walston playing the owner of a news stand who repeatedly gets knocked out when he is hit on the head by a pile of newspapers being flung from the back of a delivery truck. He temporarily loses one of his primary senses whenever he comes to. At various points throughout the movie, his character alternates between blindness, deafness, and amnesia.)Meanwhile, Tommy graduates from law school (Johnny's illicit earnings, of course, have paid for the tuition). Despite Johnny's efforts to steer him into a law firm, he goes to work for the District Attorney's office. A bit miffed that his money should be used to train a crimefighter, Johnny is nevertheless not worried for the Chief District Attorney Burr (Danny DeVito) is on his payroll. The D.A. tries to sidetrack Tommy, but he becomes a major public figure. After he holds hearings looking into Moronie's activities, the rival crime boss is deported to Sweden despite his protests that he's "not from there."Against Johnny's orders, Burr and Vermin conspire to kill Tommy. Tommy is badly injured, but survives. Divining the truth, Johnny has Burr killed, but this leaves Tommy as the new D.A.Tommy recovers, and weds his girlfriend. Vermin discovers that Dangerously is the D.A.'s brotherand Tommy promptly overhears Vermin chortling about it. Tommy confronts Johnny, who agrees to quit the life of crime. The gang, though, is not as eager and suggests Johnny may be turning state's evidence against them. Johnny denies this, and goes to turn the evidence against himself to the Crime Commissioner who Vermin has just killed, under circumstances that suggest Johnny is the killer. Not only that, Vermin steals Johnny's prized bubble gum case (formerly Dundee's cigarette case).Johnny is arrested for murder, but says he is innocent and the holder of the case is the guilty party. Tommy tries the case against him. Johnny is found guilty, sentenced to the electric chair and sent to death row. But when Vermin congratulates Tommy, and Tommy notices that he has Johnny's case, he realizes Johnny is innocent. Ma Kelly sucker punches Vermin in the crotch, and the cigarette case drops out of the stricken mobster's pocket. Ma Kelly and Tommy realize that "Johnny didn't do it."Meanwhile, his mom is using her contacts to investigate the murder. She finds the cleaning lady who is a witness to Vermin's presence. When Tommy hits Vermin with a grand jury subpoena, Vermin knows that he must kill Tommy.Johnny arrives on Death Row, where he receives rock star treatment from the starstruck warden. He receives word of Tommy's danger, and plots an escape, prevailing on the warden to move up his execution. As he is taken to the chair, Johnny assembles what looks like a tommy gun from parts handed to him by inmates. He escapes in a laundry truck driven by Lil.Johnny, through a wild and hilarious car chase, arrives at the theater where Tommy is to be killed. He shoots and wounds Vermin, saving Tommy. The governor pardons Johnny as Vermin is arrested.Back to 1935. The young shoplifter is round eyed. Having taken in the lesson that crime does not pay, he is given a kitten by the owner whom is Johnny Kelly, a law abiding pet shop owner. Johnny says "Crime doesn't pay." The kid goes on his way. Johnny, slips off his workclothes and is now dressed in a tux. He heads off in a riotous limo with Lil Sheridan where he has the last line: "Well... it paid a little!"