Counterspy was a long running series that aired over NBC, then later ABC, stations from 1942 to 1957. The episode we’ll hear today first aired December 24, 1950. Here is The Case Of The Pretty Plant.
Counterspy aired for 15 years, and brought to radio the exploits of David Harding. This episode is one of the early ones, it’s titled The Case Of The Illegal Radio Station. It first aired March 1, 1943.