In 1935, a pet shop owner catches a young boy attempting to steal a puppy, prompting him to share a story to steer the child away from a life of crime. The tale unfolds in 1910, where we meet Johnny Kelly (Byron Thames), a scrappy newsboy in New York City. After defending himself against Danny Vermin (Georg Olden), Johnny discovers that his mother, Ma Kelly (Maureen Stapleton), requires a costly operation they cannot afford. After the execution of his father, known as Killer Kelly, Ma has worked tirelessly to support Johnny and his younger brother, Tommy (Griffin Dunne), who dreams of becoming a lawyer.
As Johnny's situation grows desperate, he turns to local crime boss, Jocko Dundee (Peter Boyle), to fund his mother’s surgery, leading him to a life of crime that he initially hoped to avoid. During a robbery, Johnny adopts the moniker Johnny Dangerously, much to the chagrin of his rival, Roman Moronie (Richard Dimitri), who vows never to forget his face, comically misusing slang along the way.
Fast forward a few years, and the adult Johnny, portrayed by Michael Keaton (michael-keaton), has fully immersed himself in the dangerous world of crime, gaining the respect of his peers while keeping his real identity hidden from his beloved family. Despite the secret life he leads, both his mother and brother believe he is a legitimate nightclub owner. Meanwhile, Tommy is navigating law school, longing for a more carefree life, until Johnny intervenes with a rather bold public health message.
As tensions rise between Johnny's gang and Moronie's crew, comedic chaos ensures, including a bomb dropped from a biplane. Amid the turmoil, Johnny's romantic interest, Lil Sheridan (Marilu Henner), enters the picture, and their flirtation brings an unexpected spark to Johnny’s chaotic life.
The crime war pushes boundaries, demonstrating the absurd lengths rival gangs will go, including an outrageous attempt involving a robot and explosives. Johnny's fortunes begin to shift when Dundee retires, allowing Johnny to take the reins, but with great power comes great responsibility—especially when the D.A., Burr (Danny DeVito), turns against him.
The story escalates when Tommy’s ambition leads him to clash with Johnny’s past. Following a series of treacherous events, including an attempted murder by Burr and a near-fatal confrontation with Vermin, the danger intensifies. The climactic moments arrive as Johnny, wrongfully convicted of murder, faces the death penalty. However, his family comes together, uncovering the truth and allowing Johnny to orchestrate an audacious escape.
Ultimately, Johnny takes the leap to save his brother, demonstrating that love and loyalty surpass the shadows of crime. As the narrative wraps back to 1935, the once-stealing boy absorbs the lesson that crime doesn’t pay, while Johnny, transformed from a crime lord back to a humble pet shop owner, delivers a cheeky line about his past: > "Well... it paid a little!"
