Poul Anderson 
Flandry of Terra 
A Flandry Book

Captain Sir Dominic Flandry was a top man in the Intelligence Corps of the Imperial Terrestrial Navy. He knew that on the outer edges of the empire, civilisation was spread hideously thin. The stars faded towards barbarism, with the great evil Empire of Merseia beyond.But there were times when Flandry abandoned his senior position of command to go out into the field. Then he operated like the cool and brilliant agent he was, a ruthless, highly-trained professional. And in these three fast-moving adventures Captain Dominic Flandry shows that a space-age secret agent has to stay on top of the job – or succumb to nameless horrors.