A heavily armed interstellar spacecraft called Invincible lands on the planet Regis III, which seems uninhabited and bleak, to investigate the loss of her sister ship, Condor.

During the investigation, the crew finds evidence of a form of quasi-life, born through evolution of autonomous, self-replicating machines, apparently left behind by an alien civilization ship which landed on Regis III a very long time ago.

The protagonists come to speculate that a kind of evolution must have taken place under the selection pressures of "robot wars", with the only surviving form being swarms of minuscule, insect-like micromachines.

These swarms display complex behavior arising from self-organization and can incapacitate any intelligent threat by a powerful surge of electromagnetic interference.

Invincible's crew mounts an escalating series of attacks on the perceived enemy, but eventually recognizes the futility of their efforts.