After a century of uneasy peace, Elias Lynn, chief of the Bureau of Robotics in Cheyenne, learns that the other side may have built humanoid robots so perfect they pass for human. If such machines are already loose, they could be carrying parts of a weapon, and Lynn and the security men must find a way to catch what no one can see.
A tense Asimov robot story from Infinity magazine in 1957, with a twist worthy of the master. Download the free EPUB.