Written by Poul Anderson
Copyright 1951
First appearing in Future Combined With Science Fiction Sories, May 1951. The Betelgeuse System is in the buffer zone between the Terran Empire and the Merseian. Dominic Flandry is attending a reception on one of the planets to try to sneak in the a Merseian quarters to learn info but an enemy agent, Aycharaych, has other plans. Contained in the collection Agent of the Terran Empire.
Here are the pages I have of it.