In this, Vonnegut's first published short story, which appeared in 1950, a good-hearted professor develops the psychic ability to destroy weapons even from a great distance away. He goes into hiding and uses the "Barnhouse Effect" to destroy machines of war and armaments all over the world, leading to an uneasy world peace. To ensure that this peace is maintained, his student has also gone into hiding, to be trained to carry on the Barnhouse effect after his mentor's death.
This is a utopic story, but not without a strong edge of unease. It speaks to the deep desire of people, especially after the horrors of two world wars and the dropping of the atom bomb, to live in a world of peace, but acknowledges how fragile that peace is, even with seemingly limitless psychic power backing it up. Barnhouse imposes peace on an unwilling world, and the story makes clear that many would relish Barnhouse's death if it meant they could return to world of war and domination that, ironically, seems "safer" to them.
War and peace are thus the main themes of the story and it is to Vonnegut's credit that he delivers a tale about the seeming salvation of humans from warfare (this story was written as nuclear power was spreading) with a strong dose of anxiety. The story makes clear that a psychic weapon alone is not enough to ensure peace: the U.S. military would have misused it. The weapon rests on the conscience of the person possessing its secret, so luckily, Professor Barnhouse is, as he puts it, a "weapon with a conscience." But what if the weapon falls into the wrong hands? Weapons alone, the story suggests, are not alone what keep us safe.
It's worth noting that Vonnegut was a prisoner held by the Germans during World War II, and this lived experience informs both his desire for peace and his doubts about the human ability to achieve it. Only with eternal caution and care, the story says, will we achieve the dream of a peaceful world.