In this story, a group of villagers discover a hole that appears to have no bottom. The villagers agree to give the hole to a concessionaire who promises to fill the hole and thus remove it as a potential danger. The concessionaire establishes a "hole-filling company" and quickly sets about advertising his services. He advertises the hole as "fabulously deep" and says that it is "perfect for the disposal of such things as waste from nuclear reactors." The concessionaire explains that there will be "absolutely no above-ground contamination for several thousand years."
The concessionaire's offer is so attractive that the nuclear power plants fight among themselves for contracts with his company. Soon, lead boxes full of nuclear waste begin arriving at the hole, to be emptied into the hole one after the other. The hole initially shows "no signs of filling up" and so more and more waste arrives, including animal carcasses and the "unclaimed corpses of vagrants." The companies disposing of these things reason that disposing of them in the hole is "Better than dumping all of [their] garbage in the ocean."
At the end of the story, there falls from the sky the pebble which was the first thing to be dropped into the hole. The implication here is that all of the waste that was subsequently dumped into the hole will soon follow the pebble, and fall back to the surface of the earth.
The message of the story is that we can not simply bury our garbage or dispose of it in the oceans or carry on poisoning our atmosphere and think all the while that we can forever avoid the consequences. Eventually, we will contaminate our planet so much as to make it uninhabitable. The prospect, at the end of the story, of so much nuclear waste gushing out of the hole makes this point rather well.