Divided We Fall

". . . Divided We Fall" is a science fiction short story by American writer Raymond F. Jones, originally published in Amazing Stories in 1950. It was rewritten as a novel called Syn. Plot summary The story involves a man's return to Earth after a multi-year contract job on another planet. The Earth he comes back to, however, has undergone a devastating social upheaval. Apparently, a new race of "Synthetic Humans", or "Syns" has been created and is now intent on taking over the world. Meanwhile, the real humans are trying to destroy them. The problem is, the only way to identify a "Syn" is by a highly sensitive ECG's reading of a particular brainwave pattern, and the Syns are said to have the ability to fool the test much of the time, so they can "pass" many such tests before being detected. When they are detected, they are arrested and sent to be exterminated. In charge is a supercomputer that only the protagonist truly understands. After much adventure and tragedy, he realizes what has truly happened to humanity and his planet, as well as the computer's role. He resolves to prove his theory and save the world, or die trying.