No Laughing Matter “Joker.”

At the beginning of “Joker,” Arthur Fleck ( Joaquin Phoenix), seated in front of a mirror, hooks a finger into each corner of his mouth, and pulls. Up, then down: a grin, a grimace.

- Anthony Lane

We are meant to think of the masks, comic and tragic, that were worn by the actors in ancient Greek drama. Over the next couple of hours, those two moods will be welded together, until we can’t tell the light from the dark.

Arthur is a clown, and a would-be comic, but he’s really not funny at all. So badly does he bomb at a comedy club that footage of his set is replayed on television. That’s the joke. He lives in Gotham City, which, as everybody knows, equals New York City minus the peace and the pastoral bliss. The year, by my reckoning, is 1981, since “Blow Out” and “Zorro: The Gay Blade” are advertised on cinema marquees. Other highlights include a garbage strike. Arthur works for a clown agency, and one of his jobs is to stand on the street in a red nose and a green wig, holding a promotional sign for a local store. When some kids grab the sign, he gives chase, his enormous shoes clomping on the sidewalk. Another clown lends him a gun, for safety’s sake, but it drops out of Arthur’s costume, clattering to the floor, while he’s entertaining children in a hospital ward and singing “If You’re Happy and You Know It.” A tough gig for Arthur, who says, “I haven’t been happy one minute of my entire fucking life.”