The mayor of Gotham City is determined to tackle rising crime rates in anticipation of the city’s bicentennial and consequently commands District Attorney Harvey Dent and Police Commissioner James Gordon to ramp up police efforts. In the midst of this turmoil, reporter Alexander Knox and photojournalist Vicki Vale take on the task of investigating a mysterious vigilante known only as "Batman," who is said to be systematically eliminating criminals from the streets.
Meanwhile, mob boss Carl Grissom, aware of Dent’s crackdown on his operations, becomes suspicious when he learns that his mistress, Alicia, is romantically involved with his underling, Jack Napier. In a twisted plot of revenge, Grissom, with the help of corrupt officer Max Eckhardt, orchestrates a hit on Napier during a police raid at the Axis Chemicals plant. In a chaotic confrontation, Napier kills Eckhardt, but in the ensuing struggle, he falls into a vat of toxic chemicals, leading everyone to believe he is dead.
In truth, Batman is none other than Bruce Wayne (Michael Keaton), a wealthy industrialist haunted by the painful memories of his parents' murder at the hands of a criminal during his childhood. As Bruce begins a romance with Vicki at a charity event, he remains unaware that Napier survived the accident, emerging from it severely disfigured, with his skin turned chalk-white, hair bright green, and a sinister grin that stretches across his face. Embracing his warped new identity, he rebrands himself as "the Joker," removes Grissom from power, and takes over the very criminal empire that once held sway over Gotham.
As the Joker wreaks havoc on the city, he releases a deadly toxin named "Smilex" into hygiene products, inducing a gleeful yet fatal laughter in unsuspecting victims. Setting his sights on Vicki, he orchestrates a scene of vandalism at the Gotham Museum of Art, where Batman swoops in to rescue her. They make a quick getaway in the Batmobile, and Batman, keen on protecting the city, provides Vicki with crucial information about the Smilex threat so she can warn the residents through the Gotham newspapers.
Intent on revealing his secret identity to Vicki, Bruce's plan is interrupted by the Joker, who confronts him with the chilling line, > "Have you ever danced with the devil by the pale moonlight?" This unsettling moment escalates as the Joker shoots Bruce, who miraculously escapes unscathed due to wearing body armor. Through memories of his past, Bruce realizes that the man responsible for his parents' murders is indeed the Joker.
Vicki, inadvertently drawn into Bruce’s world, finds herself in the Batcave. After a heartfelt moment with Bruce, who confesses his identity as Batman, he sets out to destroy the chemical plant that spawned his arch-nemesis. The Joker lures the unsuspecting citizens of Gotham to a seemingly innocent parade, where he unleashes a wave of chaos by releasing Smilex gas from his enormous parade balloons—an act of sheer terror.
Batman arrives just in time, skillfully maneuvering the Batwing to save the day, but the Joker manages to abduct Vicki, taking her to the precarious heights of a gothic cathedral. In a climactic showdown atop the cathedral, Batman and the Joker engage in a fierce confrontation. As the Joker attempts to escape by helicopter, Batman grapples his leg to a heavy stone statue, leading to the Joker's dramatic fall.
In the aftermath, Commissioner Gordon unveils the Bat-Signal and reads a note from Batman, assuring Gotham that as long as crime looms, he will be there to protect the city.
