Let's Get Together
written by Isaac Asimov
published in 1957
A short story
Set in the Foundation universe
The Cold War has endured for a century and an uneasy peace between "Us" and "Them" exists. A secret agent arrives in America from Moscow with the story that robots identical to humans in appearance and behaviour have been developed by Them and that ten have already been infiltrated into America. When they get together, they will trigger a nuclear-level explosion (they are components of a total conversion bomb).
A conference of the greatest minds in American robotics is hastily convened to decide how to detect these robots and how to catch up on this technology. Almost too late, the head of the Bureau of Robotics realises that Their plan exactly anticipates this: the infiltrator robots have replaced scientists invited to this conference, and while the explosion would kill a relatively small number of people, it would precisely include America's top robotics experts, and therefore the conference must be called off, even though people are already travelling to it.
His guess is proven correct almost immediately, as ten of the scientists en route explode via self-destruct charges. However, the Bureau head wonders how They could have realized and acted upon the discovery of the plan so quickly. The truth dawns on him; he pulls a blaster and blows the secret agent's head off. The body slumps forward leaking "not blood, but high-grade machine oil."