Two planets fight a war by computer, and the casualties report voluntarily to disintegration chambers.
The Enterprise arrives at Eminiar VII, which has been at war with its neighbour Vendikar for centuries. The war is fought by computer simulation, and the people of each planet who are declared casualties walk willingly into disintegration chambers. Kirk and the crew are declared dead too.
The story is a sharp satire of civilised warfare, in which Kirk decides that the only way to end a war is to make it real again. It is remembered for the moral argument that war must remain horrible so that people will want peace, a theme common to the series.