The Dueling Machine

Dueling as a means of settling disputes has been revived by the invention of the dueling machine, which allows two adversaries to have at each other in the imaginary wrld of their choosing, with no danger to either other than humiliation and the loss of the point in dispute—until the Kerak Worlds found a way to kill with the machine. Unless a young Star Watchman can solve the mystery, the warlike Kerak Worlds will gobble up the planets of the Acquataine Cluster, murduring its leaders one at a time, and then be ready for the Terrans themselves...

Originally a short piece published as "The Dueling Machine" [with Myron R. Lewis] Analog May 1963; also as "The Perfect Warrior".