While performing a selenographic survey, Karl Jennings and James Strauss discover the crash site of a non-human spaceship. Within the wreck, they find a device which one person can use to read and manipulate the mind of another. Using the Device, Jennings discovers that Strauss is an “Ultra,” a dedicated eugenicist who would like to kill of 90% of humanity so that the remainder might lead better lives. They struggle for the Device and Jennings is fatally stabbed but manages to hide the Device somewhere on the Moon before dying. The authorities are baffled by the clue Jennings leaves behind as to the Device’s location and call on Wendell Urth to help them.

This is the final Wendell Urth story, and one of the best, largely because—unlike many mystery stories by Asimov—it isn’t puzzle driven, it’s character driven. Indeed, Urth solves the mystery in the end, not by referring at all to the mysterious clue Jennings leaves behind but simply by knowing Jennings' character. Both Jennings and Strauss are solid characters, and Jennings is particularly interesting and quirky, and, of course, it’s nice to see Urth himself one last time.

Found In

	Asimov’s Mysteries
	The Asimov Chronicles
	Complete Stories, The, Vol. 2
	Other Worlds of Isaac Asimov