Synopsis
Spoiler warning: Plot and/or ending details follow.
The story, narrated by Howard Fornoy, recounts the life of his genius younger brother, Robert. Bobby, a child prodigy whose adult interests led him to study a variety of scientific disciplines, discovered a chemical that reduces the aggressive tendencies of humans and other organisms. While doing sociological research in Texas, Bobby used crime statistics to create a sort of topographic map which displayed a geographical pattern of violent crime. Examining the map, Robert noted diminishing levels of crime centered around the town of La Plata. When he arrives to investigate, he finds that this town has never had any violent crime. Bobby is ultimately able to determine that the cause of the non-aggression is the presence of a chemical to the town's water supply, a phenomenon that is mentioned in King's earlier novel It. Even minimal exposure to the chemical will calm down an angry person or animal, and Bobby has been able to isolate the chemical and reduce it to concentrated form.
At a time of international chaos suggestive of an approaching total nuclear war, Bobby and Howard, with the aid of a volcano, disperse a large quantity of this substance throughout the world, in the hope of preventing a catastrophe. Indeed, the effects are quick and expected: a massive decrease in hostilities around the globe.
To the Fornoys' horror, there was another constant about La Plata that was not studied until after the substance was released:
a constant higher-than-normal tendency for residents to develop Alzheimer's disease, mental retardation, and premature senility.more:
http://en.wikipedia.org/wiki/The_End_of_the_Whole_Mess