In 1981, party clown and aspiring stand-up comedian Arthur Fleck lives with his mother, Penny, in Gotham City. Gotham is rife with crime and unemployment, leaving swaths of the population disenfranchised and impoverished. Arthur suffers from a medical disorder that causes him to laugh at inappropriate times, depending on social services for medication. After a gang of delinquents attacks Arthur in an alley, his co-worker Randall gives him a gun for protection. Arthur pursues a relationship with his neighbor, single mother Sophie Dumond, and invites her to his upcoming stand-up routine at a nightclub.