Manhattan is in the throes of a heatwave and in a crowded tenement house, the residents go about their daily business. Three women gossip about their neighbour, Anna Maurrant. Rumour is she’s having an affair with Sankey the milkman. Anna’s husband Frank returns home, angry that his daughter Rose is still out.
Another neighbour, Lippo Fiorentino returns home from work with an armful of ice cream cones for everybody, before Jennie Hildebrand and other high-school girls enter coming home from their graduation ceremony.
That night, young Sam Kaplan is crippling lonely. Rose is walked home by her boss, who tries to persuade her to run away with him. She refuses. Meanwhile, young Mae Jones and her boyfriend Dick McGann return home – they have been drinking and dance a high-energy jitterbug. Rose is harassed by Mae’s brother Vincent. Sam comes to her defence and is knocked down, but Rose comforts him.
The next day, Frank Maurrant leaves town on business and Sam tries to convince Rose to elope with him. With her husband gone, Anna invites Sankey up to her apartment but suddenly Frank reappears. In a blind rage, he shoots them both. Rose returns just in time to see her mortally wounded mother carried off on a stretcher.
Later that day, Frank is apprehended by the police. He shares a moment of reconciliation with Rose before being taken away. Sam again tries to persuade Rose to escape the Manhattan slums with him, but she decides she needs a clean break and must leave on her own.
As the sun sets and yet another day ends, the other residents return to gossiping and complaining about the heat.