[Steve Howland]

Family discussions over the clue brought the following realization:

Sam Spade was a detective on a radio show in the mid-40's. The show revolved around Sam Spade who solved various crimes and so forth. Spade is clearly another word for shovel, so this could be a big piece of the puzzle (or a very misleading coincidence!)

Almost all of the shows had the word "caper" in the title, which may be an important aspect, or maybe because it was a radio show there is something about radios or their frequencies involved. Maybe others who actually heard the show would know about any common themes and could enlighten us.