In Gotham City during the 1980s, a mentally troubled comedian, Arthur Fleck, struggles with his life while dreaming of a career in stand-up comedy. He works as a clown for hire, but due to his neurological disorder that causes uncontrollable laughter, he faces constant mockery and exclusion from society. Arthur lives with his ailing mother, Penny, who remains obsessed with her past employment for the wealthy Wayne family. His life gradually starts unraveling from a confluence of oppressive forces—poverty, isolation, and a cutthroat, uncaring society—that ignore and mistreat the vulnerable like him. This crumbling state pushes him to seek connections through his idol, talk show host Murray Franklin, who represents the success Arthur yearishly desires.

As Arthur’s mental health further disintegrates, exacerbated by the discovery of troubling secrets about his family history, he transforms, embracing a more anarchic and violent persona. Incidents of public humiliation and personal betrayal catalyze his descent into the darker parts of human psyche. Simultaneously, Gotham City itself spirals into chaos as economic disparity and rampant crime feed public unrest. Arthur finds himself increasingly at odds with the world, culminating in acts of reprisal against those he believes have wronged him. His personal turmoil reflects the larger social upheavals shaking the decaying city, foreshadowing a broader eruption of violence that challenges the very foundations of Gotham's fractured society.