Agent Of Vega
Written by
James H. Schmitz
Copyright 1949
Published in Astounding Science Fiction, July 1949. Collected in
An alien species of 'noncorporeal parasites' called the Ceetal are engaged in a systematic conquering of the galaxy. These creatures can take over a human body and rule it from the inside and they have already inhabited the leaders of nearly a thousand star systems. Zone Agent Iliff is sent to the planet Gull where Zone Agent Trainee Pagadan, a non-human telepath, has uncovered the plot and together they must find a way to stop it.