Nick Carter Radio Serials
The old time radio series "Nick Carter, Master Detective" had a short run as a serialized adventure. Few of these episodes exist.
This recording is part of the Old Time Radio collection.
Chapters
Reviews
Half-hour Nick Carter shows are available, too!
Old as Old Time Radio
There are a great number of the half-hour available in the Internet Archive. To find them: In the Search field: Nick Carter In the Media Types field: Radio Programs There are more than 90 shows there. UPDATE November 18, 2014. Thanks Greybelt, for the correction. I did not make the distinction between the serialized version and the half-hour "stand alone" shows. I hope more of the serials will show up.
Nick Carter serials vs half-hour shows
Greybelt
It's correct that there are many, many of the half hour Nick Carter shows available. The serialized version, however, did not last a very long time, and copies have been elusive.