The Uninvited Guest
Written by
Christopher Anvil
Copyright 1967
Printed in Analog, March 1967. Reprinted in the collection
The large structure appeared out of nowhere one day. The first man to spot it thought it might be a mirage in the heat of the day so he threw a rock at it and the rock shot back at him with the force of a .45. Since this was happening near a military missile-test site, the General running the facility contacted Richard Verner to help figure out what it was and what to do with it.