A suburban dinner party is interrupted by a bulletin warning of an impending nuclear attack. As the neighbors scramble to prepare themselves, they turn against the one family that installed a permanent bomb shelter.
Although a great many episodes of "Twilight Zone" were philosophical and raised ethical points (a big part of what made it great), this episode has the distinction of being one of only four to be strictly realistic in nature -- no science fiction or fantasy elements can be found.
This realism is what made the story both memorable and powerful. Rod Serling, in an interview with Bob Crane, claimed that shortly after the episode aired, he received 1300 letters within two days from folks who were both delighted and terrified, and from those who understood the message and those who obviously did not.
We have a tale of the haves versus the have nots, though not necessarily with money -- with safety and shelter. The episode shows that hysteria and panic can easily turn one group against he other -- a situation every bit as dangerous as an atom bomb.
Further, the ethical elements are compounded by having the lead character be a medical doctor. If you have a shelter, are you obligated to allow neighbors in, or wise to leave them out? And with a doctor the question must be asked: are they to be held to a higher standard because they are caregivers who are loyal to the Hippocratic Oath?
Of course, it could reasonably be argued that saving your family and excluding others is saving some people rather than risking the lives of all when oxygen runs low... but then, maybe your own kids are not as worth saving as someone else? The ethical elements are many.
Interestingly, in the Crane interview, Serling was conflicted on the whole idea of fallout shelters. He said his family thought about it, but ultimately decided against it -- not because of the ideas shown in the episode, but because of what he feared would happen to the survivors, left to scavenge like wild beasts. They might survive, but is that kind of survival worth having?