Cassen's family lives in a lavatory because they are poor. All he owns is a three-wheel truck that he earns a meager living with. He has to pay a bill tonight or lose it, and no one is interested in telling him precisely how much he owes or collecting it because it is Christmas Eve. Everyone is more intent on the local "Win an evening with a movie star" pageant, or making sure they get a good-looking poor person to eat Christmas diner with them, because that's a public charity campaign that Franco is pushing at the moment.
Luis García Berlanga's film is about a Spain where the well-to-do care only about appearances, and while they may attempt to perform acts of charity, they fail to accomplish anything worthwhile because there is no charity in their hearts. It's a very large cast that roams through a dozen households, but always returns to Cassen who's promised this ad that an imposed on, and will, the audience becomes aware, will come aay with nothing, not even a Christmas dinner, because the upper class has to go to midnight mass. It's a wry and ultimately despairing look at Franco's Spain.